WO2009112040A2

WO2009112040A2 - Brushless real dc machine

Info

Publication number: WO2009112040A2
Application number: PCT/EG2008/000012
Authority: WO
Inventors: Wagih Abd Eltawab Ghannam
Original assignee: Wagih Abd Eltawab Ghannam
Priority date: 2008-03-11
Filing date: 2008-03-11
Publication date: 2009-09-17
Also published as: EG25556A; WO2009112040A3

Abstract

The brushless real dc machine consists of:- 1- Stator which has two stators for two adjacent machines in the same frame and each machine has its rotor which produces its magnetic field. The stator consists of: a- Front part and rear part which contain the slots and teeth and winding b- Upper and lower yokes connecting between the front and rear parts. Set the winding in the front part as following: insert one of the two coil sides in a slot of the right machine and insert the other side in a slot of the left machine and so on for the other slots then connect between the coils in series or parallel according to the design then set the coils in the rear part in the same manner. Then insert each rotor in its stator. 2-Each rotor has the field coil in the middle between the north pole and south pole. The north occupies its space in the front part (or rear) and the south in the rear part (or front) in the same machine. Adjust the direction of the field and the current in the windings in the front and rear parts of each machine to obtain two rotors rotating in the needed directions. 3- The two exciters: - each rotor is excited from its own brushless exciter attached to the rotor shaft. Each exciter consists of:- 1- three phase wound rotor induction machine 2- three phase rectifier connected between the rotor winding of the induction machine and the main field coil

Description

BRUSHLESS REAL DC MACHINE

Technical Field

The electrical machines

Background Art

The conventional dc machine which consists of: 1- The Stator has:

- Main field poles to produce the magnetic field

- Yoke between each two adjacent poles to transfer the flux between them

- Interpoles between the main poles to limit the bad effect of the armature reaction

2- The armature loaded on a shaft and has:

- The main machine windings

- The Commutator loaded on the same shaft and connected to the main winding terminals

3- The Brushes are touching the commutator to transfer the power from or to the armature winding

Disadvantages of the conventional dc machine

1- The transfer of electric power is being through the brushes to or from the commutator segments by touch, but electrically, the best case is to transfer the power through the fixed terminals as the case of the other electrical machines

2- Need extra maintenance and maintenance cost with respect to the induction and brushless synchronous machines

3- The commutation problem which causes the following:-

- Limits the maximum out put power that can be taken from the machine

- Limits the maximum speed which the machine can be designed (especially the medium and large rating) - Sparks may be occur between the commutator and the brushes leading to damage them

4- The center fugal forces affecting on the armature winding in the slots and the over hang coils will affect on the maximum speed which the machine can be designed

5- The armature core subjects to the following frequencies:

- The alternating current in armature windings

- The magnetic field reversals during the rotation of armature under the poles. These frequencies increase the core losses (eddy and hysteresis losses) which lead to increase the temperature rise and reduce the efficiency

Disclosure of the invention

Advantages of the brushless real dc machine

The brushless real dc machine is for getting the perfect characteristics of the dc machine without its problems but, with the following advantages: 1-The armature winding exist in the stator (instead of the rotor) but, the field coil will be on the rotor and fed from a brushless exciter on the same shaft. This step will give extra advantages as the following:

- The machine will be free from the brushes, the commutator and the interpoles

- The armature windings ended with two fixed terminals connected directly to a dc supply in the motor mode or to the load in the generator mode.

- A good cooling for the rotating field coil

- It is available to use the best cooling method, which is the flowing of the cooling liquid or gas directly into the armature coils.

- It is available to control the speed in steps by varying the armature winding connections (series and parallel). This is considered one of the speed control methods without drive equipment 2- Low maintenance as the induction and brushless synchronous machines

3- It is available to design the machine with the desired output without limitation because there is no commutation

4- It is available to design the machine with the desired speed without limitation because:

- No commutation

- The field coils and the poles on the shaft are in a cylindrical form and have the same axis of the shaft (no salient parts which limit the speed)

5- The machine is free from the frequencies (flux reversals and armature ac current) leading to:-

- Minimum core losses (eddy and hysteresis) then high efficiency.

- The thickness of the magnetic steel laminations may be increased to reduce the laminations cost affecting on the final machine cost.

Construction of the machine.

As in fig. (1), the machine consists of two adjacent machines in the same frame and each of them has its own rotor.

The stator is assembly from three parts:-

1- The front 2- The rear 3- The middle

Without the metal frame, the two machines are appearing as in fig. (2) which has,

(2.1) is the left machine and (2.2) is the right machine and every one has a rotor as in fig.(6).

Fig. (6) shows the rotor which produces the magnetic field. Each rotor has the north pole (6.1) , the south pole(6.2) and the pole body (6.3) which has the field coils. Construction of one of the two stators:-

Fig. (3) shows that, the stator of one machine consists of three parts made from steel laminations. The part (3.1) is the front and will be occupied with the north pole.

The part (3.2) is the rear and will be occupied with the south pole.

The part (3.3) is the upper yoke which receives the flux from the front then deliver it to the rear.

The part (3.4) is the lower yoke which receives the flux from the front then deliver it to the rear.

Construction of the front (or rear):-

Both front and rear are similar and consists as in fig. (4) of:-

(4.1) is a stator contains closed slots and the inner space to enclose its pole.

(4.2) is the connection part which delivers the flux from the stator (4.1) to the upper, yoke and made from steel laminations perpendicular to that of the stator (4.1)

(4.3) is as (4.2) but delivers the flux from the stator to the lower yoke.

Assembly of the three parts of the stator individually As in fig/5):- The fronts of the right and left machines (5.1) are assembled in the same frame. The rears of the right and left machines (5.2) are assembled in the same frame. The upper and lower yokes of the right and left machines (5.3) are assembled in the same frame. Then the whole stator is reassembled to be as in fig. (1) after placing the coils in its slots.

The magnetic circuit and flux paths.

By assembly of one rotor and its stator then make section in a side view as in fig.(7) which shows the following :-

(7.1) is the air gap between the rotor and stator

(7.2) is a front (7.6) is the north pole (7.3) is a rear (7.7) is the south pole

(7.4) is the upper yoke (7.8) the shaft

(7.5) is the lower yoke (7.9) is the field coil

Placing the coils in the stator slots.

Before assembly of the three parts of the whole stator,

1- Place the coils in the total front as in fig. (8) as the following:

Insert one side of a coil in slot number one of the right machine then insert the second side of the coil in slot number one of the left machine then connect between the two sides. Repeat this procedure with another coil between both slot number two of the right and left machines and so on.

2- Place the coils in the total rear as the front as in fig.(9).

Adjusting the current directions in motor mode.

1^st - In the total stator front as in fig. (10) connect between the coils in series or in parallel (according to the design) to get two terminals and energize them such that the current direction in the right stator is entering the slots as in (10.2) therefore the current direction in the left stator is getting out from the slots as in (10.4) then energize the field coil of the right rotor such that the pole in the right front is north and its direction is (10.1) and energize the field coil of the left rotor such that the pole in the left machine is south and its dire, is (10.3).

By applying the left hand rule on the illustrated system, the two rotors will rotate clockwise.

2^nd - The total stator rear as in fig. (11).

Connect between the coils in series or in parallel (according to the design) to get two terminals and energize them such that the current direction in the right rear is getting out from the slots as in (11.2) therefore the current direction in the left rear is entering the slots as in (11.4) then, already due to the last procedure, the right rotor field coil is energized and will give south pole in the right rear of the machine and its direction is (11.1). Also, the pole in the left rear of the machine is north and its direction is (11.3).

By applying the left hand rule on the illustrated system, the two rotors will rotate clockwise also.

** The result is, the two shafts rotate clockwise.

If needed to reverse the direction of one of them, reverse the energizing of one of the two rotors only.

The brushless exciter of the machine in the motor mode.

Each rotor has an exciter illustrated as below:-

As in fig. (12) the field coil (12.1) terminals passed through a slot on the pole radiator (12.3) to be connected to the exciter rotor winding.

The exciter of each machine consists of:-

1- Three phase stator (12-5) fed from automatic voltage regulator

2- Three phase wound rotor (12-6) connected to a three phase rectifier

3- Three phase rectifier (12-4)

Note: - One AVR only to feed the two exciters

The operation procedure in motor mode

1- At starting, a three phase supply applied on the exciter stator through automatic voltage regulator (AVR which may be an ac chopper) to produce a rotating magnetic field which induces a three phase e.m.f. on the exciter rotor (the exciter operates as a motor in the same direction of the main machine) then rectified by the rectifier (on the shaft) to inject dc current in the main field coil. At this moment the stator winding of the main machine is energized from its dc supply.

* The exciter torque will be added to the torque of the main machine to reduce the starting time and starting current. 2- When the shaft reach an a advanced speed, the relative speed between the rotating field and the exciter rotor got small leading to small e.m.f. which is not enough to provide the main field with its heavy excitation to face the load variations. In order to increase the relative speed again, the AVR will reverse the phase sequence applied on the exciter stator (the exciter will operate as a generator) to get a large relative speed between the exciter rotor and the rotating field which increases the exciter rotor e.m.f. but AVR will control the voltage magnitude applied on the exciter stator for keeping the needed excitation of the main field. * The two shafts of the machine may be connected to a gear box to obtain one shaft (or more) according to the load type

The operation procedure in generator mode

The two shafts of the machine are connected to a gear box to obtain one shaft as in fig. (13) to be connected to the turbine.

When the generator reaches the rated speed, the AVR feeds the exciter stator to produce a rotating field in the opposite direction of the rotating shaft. The rotating field induces an e.m.f. in the exciter rotor then rectified by the three phase rectifier which injects dc current in the main field coil.

Note: - To obtain the resultant voltage of the whole machine, the direction of the field and the rotation of the two rotors will subject to the right hand rule.

Brief description of the drawings

Fig. (1) shows the whole machine stator in the same frame. (1.1 ) the front (1.2) the rear (1.3) the middle

Fig.(2) shows the stator without the frame.

(2.1) the left machine (2.2) the right machine

Fig.(3) shows the construction of one of the two adjacent machines.

(3.1) the front (3.2) the rear

(3.3) the upper yoke (3.4) the lower yoke

Fig.(4) shows the construction of the front.

(4.1) a stator (4.2) the connector between upper yoke and stator ,

(4.3) the connector between the lower yoke and stator.

Fig.(5) shows the three parts of the machine.

(5.1) the total machine front

(5.2) the total machine rear

(5.3) the total machine middle

Fig.(6) shows one of the two rotors.

(6.1) the north pole (6.2) the south pole (6.3) the coil placing

Fig. (7) shows the magnetic circuit and the flux paths.

(7.1) the air gap (7.2) the front (7.3) the rear

(7.4) the upper yoke (7.5) the lower yoke (7.6) the north pole (7.7) the south pole (7.8) the shaft (7.9) the main field coil Fig.(8) shows the coils between the two stators in the front.

(8.1) closed slot number (11) in the left machine.

(8.2) closed slot number (11) in the right machine.

(8.3) an over hang coil

Fig.(9) shows the coils between the two stators in the rear.

(9.1) closed slot number (11) in the left machine.

(9.2) closed slot number (11) in the right machine.

(9.3) an over hang coil

Fig.(lO) shows the directions of:-

- The current in the slots of the machine front

- The fields

- The rotations

(10.1) the direction of the magnetic flux in the right machine.

(10.2) the current enter the slots

(10.3) the direction of the magnetic flux in the left machine.

(10.4) the current getting out

Fig. (11) shows the directions of:-

- The current in the slots of the machine rear

- The fields

- The rotations

(11.1) the direction of the magnetic flux in the right machine.

(11.2) the current getting out

(11.3) the direction of the magnetic flux in the left machine.

(11.4) the current enter the slots Fig.(12) shows a section in the rotor loaded with the coil and attached to the exciter (12.1) the field coil (12.2) the north pole

(12.3) slot on the pole face (12.4) three phase rectifier

(12.5) the exciter stator (12.6) the exciter rotor

(12.7) automatic voltage regulator (12.8) the shaft

Fig.(13) shows a plan for the brushless real dc machine connected to the gear box . ( 13.1 ) the brushless real dc machine ( 13.2) the exciter of the left machine

( 13.3 ) the exciter of the right machine (13.4) the gear box (13.5) the shaft of the left machine (13.6) the gear of the left machine shaft

( 13.7) the shaft of the right machine ( 13.8) the gear of the right machine shaft

( 13.9) the output gear of the gear box ( 13.10) the output shaft of the gear box

Fig.(14) shows a section in the side view of the machine which enclosed by its frame

Fig.(15) & (16) show the basic dimensions of the machine

Ic is the path length of the magnetic field in the stator core ds is the depth of the slot closing hs is the slot length

It is the tooth length

Dss is the inner diameter of the stator

Iy is the path length of the magnetic field in the yoke

Ig is the air gap length lpr is the path length of the magnetic field in the pole radiator hy the yoke height hf is the height of the field coil Dr is the rotor diameter

L is the pole radiator length he the core height

Lp is the length of the pole body Do the shaft diameter Best mode for carrying out the invention

The following points will show how to make the machine parts: A- The stator

1- Fig. (4) is the front part of one of the two adjacent machines as illustrated before.

- The part (4-1) will be made from laminations as the figure.

- The parts (4-2) and (4-3) will be made from laminations its directions is perpendicular to the part (4-1)

2- In fig. (3), the parts (3-3) and (3-4) will be made from laminations as the figure.

3- In fig. (5), the two front parts are assembled by the tight metal frame in (5-1) and so on for the two rear parts in (5-2). The upper and lower yokes are also assembled by a tight metal frame in (5-3)

4- After placing the winding in the front and the rear of the machine, the three parts (front, rear and middle) is ready to be assembled as described before.

B- The rotors

Each one of the two rotors is a solid as the fig. (6)

C- The exciters. Each exciter is a three phase wound rotor induction machine, its rotor windings are connected to a three phase rectifier which feeds the main field coil.

After illustrating the machine parts, the design steps are as the following:- DESIGN

A) Stator

As illustrated that, the machine has similar four stator cores, so, the design will be done for one only and repeated for the others.

When start the design steps, the power in KW for one core is KW / 4

Where, KW is the sum of the main machine and the exciter powers, and the supply voltage of this part is V = Vs / 4 but the speed in rpm is still n

B- Rotor

As illustrated that, the machine has similar tow rotors, so, the design for one only then repeated for the other.

Take into account that the rotor will be loaded with the field coil for the front and rear stator cores for one machine

Fig. (15) and fig. (16) illustrate the basic dimensions

1- Calculate the minimum shaft diameter Do according to the power and speed of the machine and the mechanical properties of the shaft material for example : Do = 5.5(Kw/r.p.s.) Ψ then get the shaft cross section area Ao

2- Choose the ratio of minimum tooth width to the slot pitch K= Wt/τ in range of (0.5 - 0.62) or according to the best experience of the manufacturer

3- Assume that the air gap is small that the rotor diameter is the same of the stator. From this, the initial length of the stator core is

Li = (Ai/K)/O Where: Ai = π (0.5Di) ²

Di is the rotor diameter

Ai is the cross section area of the rotor

Ci the circumference of the rotor

Li = Di/4K 3- It is known that, the output equation is Di²Li = (KW/r.p.s.) (1000/ π² Bav ac) From the above Di³ = (KW/r.p.s) (4000K/ π² Bav ac) then get Li and Ai

4- The pole area is Ai and will be loaded with the magnetic flux but the shaft area Ao will be subtracted from Ai so the new area is Ap = Ai+ Ao and the new diameter is Dp = 2(A_P/ π) Ψ

5- Let the height of the field coil is hf = 0.05Dp

6- The final rotor diameter is Dr = Dp + 2hf where hf is the height of the field coil

7- The stator diameter is Dss = Dr + 21g where Ig is the air gap length

8- The air gap will be determined by the mechanical consideration as speed, vibration,... etc as the manufacturer experience

9- In order to close the slots let ds = 5mm then, the effective stator diameter is

Ds = Dss + 2ds

10- The final length is L = Li/€ where € is the ratio of Ds/Di 11-Take the length of the pole body L_P = 0.9 Dr

12- The e.m.f. per conductor ec = BLv when v = Ds π n/60

13- Number of conductor in series is Zseries = V/ ec

14- The slot pitch τ normally in the range of (2 — 4)cm

15- Number of slots is Ns = πDs/ τ and Zs is the number of conductors per slot 16- Slot loading < 1500 A

17- Make a balance among Ns , Zseries , τ and slot loading then get the number of parallel paths (a)

18- The current per conductor is Iz = Ia /a where Ia is the armature current 19- The conductor cross section area is Aco. = Iz /J where J is the current density A/mm²

20- The tooth width is Wt = K τ then slot width Ws = τ - Wt

21- The slot depth hs may be increased to enclose the coil bars with its insulations without the consideration of the reactance voltage limitation because this machine is free from the frequency

22- The gap flux density in this machine is Bg = Bav the average flux density because the flux is uniformly distributed on the inner stator surface

23- Calculations of ampere turns for the magnetic circuit

23.1- Ampere turns of air gap ATg = Φ lg/μ Ag where Ig is the air gap length, μ is the air permeability, Ag is the average area of the air tube passed radial by the flux. Ag = π (Dr+ Ig) L then Φ is the total pole flux = Bg Ag

23.2- Ampere turns of teeth ATt

Bt = Φ / L X Wt then get Ht from B-H curve

ATt = 2Ht It It = ( hs + ds) ,the sum of tooth length and slot closing length, Ampere turns of teeth is multiplied by 2 for getting the Ampere turns of teeth in front and rear stators

23.3- Ampere turns of the core ATc

Bc =(Φ/2) / L we where we is the core width = (Ds + 2hs + 2dc) then, get Hc from B-H curve and get ATc = HcIc

Ic is the mean core length depends on the vertical distance he.

The stator over hang coils which pass from the right machine to the left at the front and behind the stator core will affect on the value of he. The number of these coils is Ns/3 and will be arranged in horizontal distance of Lp/2 and vertical dist. of he (in other words, a rectangle has length of Lp/2 and width of he )

The number of coils in horizontal is the number of columns Nh but the number of coils in vertical is the number of rows Nv.

Get the integer of Nh = (Lp/2) / kiWs where ki is the minimum space factor, may be 2, then get the number of rows Nv = (Ns/3)/Nh then get he = Nv hs ki, Then get Ic = he + (Ds+2hs)/4

23.4- Ampere turns of the yoke ATy = HyIy, where Ly is the mean length of the yoke = Lp + L + hy.(It is a good choice if By =1.7 in order to minimize ATy & hy) The cross sectional area of one yoke Ay = (Φ/2) /1.7 then hy = Ay / we

23.5- Ampere turns of the pole body ATp = Hp Lp and Bp = Φ / Ai

23.6- Ampere turns of the pole radiators ATpr = 2Hpr Lpr

Where B_pr = Φ / L π ( Dp + hf ) and 21pr is the sum of mean length in the two pole radiators = 0.5( Dr - Do ) + L

23.7- The no load ampere turns of the field is:

ATfo = ATg + ATt + ATc + ATy + ATp + ATpr

23.8- The full load ampere turns of the field may be taken as ATn=ATf₀ + ATa

Where ATa is the armature ampere turns = Ns Zs Iz / 2 Industrial applicability

1- Many applications which need the dc machine characteristics as rolling mills

2- The applications which need the dc machine but not use it because of its maintenance and commutation problems

3- The applications which need the dc machine of large ratings and speeds but were not applicable with the conventional dc machine

Claims

CLAIMSThe whole system of "BRUSHLESS REAL DC MACHINE" which includes the following:-1- The stator which includes:

1.1- the front, consists of two adjacent stators (contain the slots and teeth) existing in the same metal frame.

1.2- The rear, consists of two adjacent stators (contain the slots and teeth) existing in the same metal frame.

1.3- The upper and lower yokes (in the same metal frame) which complete the magnetic circuit between the front and the rear of the machine.

2- The placing of the coils in the front of the machine and the rear also, which is by inserting one of the coil sides in a slot of the right machine then inserting the other side in a slot of the left machine and so on.

3- The two rotors. Each of them is solid and has the field coil in the middle between the north pole and the south pole and the group has the same axis.

4- The two exciters. Each of them consists of:

4.1- Three phase stator fed from automatic voltage regulator

4.2- Three phase wound rotor connected to a three phase rectifier

4.3- Three phase rectifier to feed the main field coil

5- Automatic voltage regulator which may be an AC chopper and has the ability to inverse the phase sequence.

6- The mentioned design procedure