AU714576B2

AU714576B2 - Method for operating a generator and circuit for carrying out the method

Info

Publication number: AU714576B2
Application number: AU35415/97A
Authority: AU
Inventors: Knut Bartsch
Original assignee: Ficht GmbH and Co KG
Current assignee: Ficht GmbH and Co KG
Priority date: 1996-07-10
Filing date: 1997-07-04
Publication date: 2000-01-06
Anticipated expiration: 2017-07-04
Also published as: DE19627816A1; AU3541597A; JP2000503839A; TW354437B; WO1998001931A1; EP0910888B1; CA2260039A1; EP0910888A1; DE59708382D1; ATE225577T1; CA2260039C

Abstract

The invention relates to a process for operating a generator with a plurality of generator windings in which a voltage is induced. When rotational speeds or voltage supply are low, at least two of the generator windings are connected in series and when rotational speeds or voltage supply of the individual generator windings are higher, said windings are connected in parallel thereby reducing the voltage of the generator. The overall voltage of the generator is consequently easily maintained in a predetermined range without the need for complicated voltage regulators. High output voltages are also produced when rotational speeds are low and operate electrical apparatus, in particular fuel injection devices. The process according to the invention can also be used for other active voltage sources, such as solar cells, batteries etc. which do not provide a constant voltage supply but have consumers which require a substantially constant voltage.

Description

1 Ficht GmbH Co. KG Spannleitenberg 1 D-85614 Kirchseeon Method for operating a generator and circuit for carrying out the method A known high-power generator is illustrated diagrammatically in a simplified manner in Figure 8 and Figure 10. This generator has a six-pole stator 1 and a separately excited rotor 2. Stator coils 3a, 3b are arranged on the poles of the stator 1, a voltage being induced in said coils in the event of a rotary movement of the rotor. Two types of stator coils 3a, 3b are provided, namely first stator coils 3a having a thin wire and many windings and second stator coils 3b having a thick wire and half as many windings as the first stator coils 3a.

The first stator coils 3a are dimensioned in such a way that their current output commences at about 1000 rpm.

On account of their dimensions and their number of turns, their current output is limited to about 35 A at 8000 rpm (dashed line in Figure 9) The second stator coils 3b start to output current only at about 2000 rpm but are designed for a high current output. With full excitation, they permit a current flow of up to 75 A at about 8000 rpm.

As shown by the circuit diagram shown in Figure 10, the individual coil types are connected in parallel, with the result that currents generated in the two stator coil types 3a, 3b are added together. Consequently, a maximum current output of 35 A 75 A, that is to say 2 110 A in total, can be obtained with this generator.

This generator achieves a high power output with a small structural size, only relatively slight heating occurring during operation up to about 60 amperes since the second stator coils 3b are loaded only with half the maximum current.

This generator is unsuitable for rotational speeds of below 1000 rpm since the voltage generated is so small that no appreciable current flow can occur at the loads. If the first stator coils 3a were designed in such a way that they effected a sufficient voltage output at rotational speeds of 500 rpm, for example, then their numbers of turns would have to be distinctly increased and a correspondingly thinner wire would have to be used. As a result of this, the limit current would be drastically reduced and these coils would output no appreciable contribution to the total current during normal operation.

In the case of motors having a manual starting device, such as boat motors, for example, very low rotational speeds of 150 rpm, for example, occur during the starting phase. Such "small" motors are equipped with electronic controllers and/or injection devices, with the result that batteries have to be provided even with the use of manual starting devices since, from 150 rpm, known generators do not generate a sufficiently high voltage of about 10 volts to be able to operate these electrical devices, in particular injection devices.

If such a generator were designed in such a way that it already generated a voltage of 10 volts at 150 rpm, i would indeed deliver a suitable voltage at low Srotational speeds but, since the voltage that is output 3 is proportional to the rotational speed, a voltage of 430 volts would be generated at 6500 rpm, for example.

Components for such high voltages are very expensive.

In the case of generators for motor vehicles, the voltage is regulated to a desired value by means of a specific regulating device. However, such a voltage regulator signifies a considerable technical and financial outlay, in particular in order to regulate voltage ranges of this magnitude.

The invention is based on the object of providing a method for operating a generator which enables operation of a generator even at very low rotational speeds, in which case the voltage generated by the generator can also be realized at high rotational speeds using commercially available components.

Preferably, the method according to the invention intends to make it possible to operate a generator from rotational speeds as low as 150 rpm. Furthermore, the invention is based on the object of providing a circuit for a generator which enables a generator to be operated over a large rotational speed range and, in particular, at low rotational speeds.

The object is achieved by means of a method having the features of claim 1 and a circuit having the features of claims 5 and 13.

According to the method of the invention, generator coils of a generator are connected in series at low rotational speeds, with the result that the voltage induced in the coils is added. At high rotational speeds, these generator coils are connected in parallel, with the result that the currents induced in the coils are added together and the total voltage output by the generator is reduced.

4 This transition from a parallel circuit to a series circuit is the essential principle behind the present invention because the voltage that is output can be kept in a desired range in a simple manner by this means.

The invention is explained in more detail, by way of example, with reference to the drawing, in which, diagrammatically and in a simplified manner: Figure 1 Figure 2 Figure 3 Figure 4 shows a schematic sketch for the method according to the invention using six DC generator units, diagrammatically shows the structure of a DC generator unit, shows a circuit with which the method according to the invention can be carried out, shows a modified circuit, shows a voltage profile for a generator which is operated by the method according to the invention and has four circuit stages, shows a switching arrangement without active switching elements, shows further switching arrangements without active switching elements, diagrammatically shows a stator and a rotor of a known generator, Figure 5 Figure 6 Figure 7 -73- {i-u A Figure 8

I

5 Figure 9 shows a diagram of the current output of the generator from Figure 8, and Figure 10 shows a circuit with which the generator illustrated in Figure 8 is operated.

Using the method according to the invention, generators are operated in such a way that they output an output voltage lying within a predetermined range, without a complicated voltage regulator.

As is known, generators comprise a stationary stator 1 and a rotating rotor 2. Generator coils 3 are usually arranged on the stator i, voltage being induced in said coils in the event of a rotation of the rotor 2.

In order to facilitate the illustration of the inventive principle, three coils 3 of a generator which are connected to a DC generator unit 4 (Figure 2) will be considered.

The three coils each generate a voltage whose phases are offset by 1200 in accordance with a three-phase current. The three coils 3 are connected to a threephase rectifier constructed from six diodes, said rectifier being known per se. Consequently, this

DC

generator unit 4 constitutes a DC source which generates a current IGG and a voltage UGG during operation of the generator.

According to the method of the invention, these

DC

generator units 4 are connected in series at low rotational speeds of the generator and are connected in parallel in stages at higher rotational speeds. Figure 1 illustrates the method according to the invention using four circuit stages I-IV, six DC genera:or units 6 4 being shown which produces [sic] a total voltage at the generator of UG 6 UGG in the event of a straightforward series circuit first circuit stage I) of all six DC generator units 4.

If the rotational speed at which the rotor of the generator is rotated increases, then the voltage generated in the individual DC generator units 4 also increases. The straightforward series circuit of the first circuit stage I is therefore changed over into a parallel circuit of in each case three DC generator units 4 second circuit stage II), with the result that the total voltage becomes UG 3 UGG. As a result of this, the voltage of the individual DC generator units 4 which rises with higher rotational speeds is reduced.

In the event of a further voltage rise, the six DC generator units 4 are connected in parallel to form three respective pairs of DC generator units 4 third circuit stage III). A total generator voltage of UG 2 UGG is produced in this case.

In a last circuit stage IV, all the DC generator units are connected in parallel, with the result that the total voltage UG 1 UGG.

The voltage profile U of a generator whose DC generator units 4 or coils are connected in accordance with the four circuit stages I-IV illustrated in Figure 1 is illustrated in Figure 5, the rotational speed N at which the generator is operated being entered at the same time.

As is shown in Figure 1, the generator is operated with four circuit stages I-IV, it being the case that the If r 7 generator voltage UG rises very steeply with an increasing rotational speed during the first circuit stage I since all the DC generator units 4 are connected in series. A voltage of 10 volts is already obtained at about 150 rpm. At a voltage value of about volts, a changeover is made to the second circuit stage II, with the result that the generator voltage

U

abruptly falls to about 25 volts.

The voltage then rises again with an increasing rotational speed, a changeover to the next circuit stage III being made at about 35 volts, for example, as a result of which the voltage of the generator again falls to a value of about 25 volts.

The changeover to the last circuit stage IV is made at about 40 volts, as a result of which the generator voltage is reduced to about 25 volts once again. The maximum voltage of about 40 volts is achieved approximately at 6000 rpm. Consequently, the method according to the invention makes it possible to keep the output voltage of a generator in a predetermined range of about 20 to 40 volts, for example, simply by changing over the arrangement of the DC generator units 4. Since a plurality of DC generator units 4 are connected in series at low rotational speeds, an output voltage which enables operation of electrical equipment, in particular injection devices or injection pumps and the like, is already obtained at extraordinarily low rotational speeds of 150 rpm, for example.

A circuit which is suitable for the method according to the invention is illustrated in Figure 3.

This circuit has two main lines 5, 6, between which -e -V \UTC /1 8 DC generator units 4 are arranged. The DC generator units 4 are connected by their positive output to the main line 5 via a respective branch line 7, and are connected by their negative output to the other main line 6 via a respective branch line 8.

Branch line switches 9, 10 are respectively arranged in the branch lines 7, 8 and can interrupt the current flow in the individual branch lines 7, 8. Each branch line 7 connected to a positive output of a DC generator unit 4 is connected via a respective cross-connection line 11 to a branch line 8 arranged at a negative output of a different, preferably adjacent,

DC

generator unit 4. The cross-connection lines 11 consequently connect the positive output of one DC generator unit 4 to the negative output of another, adjacent DC generator unit 4. The cross-connection lines 11 are arranged at the branch lines 7, 8 in each case in the region between the DC generator units 4 and the respective branch line switches 9, 10. A switch 12 is arranged in each of the cross-connection lines 11.

In this circuit, two adjacent DC generator units 4 are respectively connected in series by the closing of the switch 12, arranged between them, of a cross-connection line 11, the branch line switches 9, 10 of the branch lines 7, 8 which are connected to this cross-connection line 11 having to be opened. In this way, any desired number of DC generator units 4 can be connected in series, the series-connected DC generator units 4 being connected, at the outer DC generator units 4 thereof, to the main lines 5, 6 via the corresponding branch lines 7, 8 by means of two branch line switches 9, If all the switches 12 of the cross-connection Lines are open and, correspondingly, all the branch line -t h b a n h Un Ct< 9 switches 9, 10 are closed, then all the DC generator units 4 are connected in parallel. This corresponds to the fourth circuit stage IV in accordance with Figure i.

In a simplified embodiment of the invention (Figure 4) all the branch line switches 9, 10 of the branch lines are replaced by diodes 13. Only the branch lines 7, 8 at the outermost DC generator units 4, at which no cross-connection lines 11 are present, are constructed as continuous lines free from switches or diodes. The individual switches 12 are consecutively designated by letters A to E.

If one of the switches 12 is closed, then the DC generator units 4 adjacent to the switch 12 are connected in series via the cross-connection line 11 in which the switch 12 is situated. The increased voltage potential turns the nearest diode on and thus increases the potential difference of the main lines 5, 6. All the other diodes turn off automatically. Consequently, all the further diodes 13 become passive switching elements which interrupt further parallel-path currents.

If the switch 12 is opened again, the current flow runs through the diodes 13 again, and the DC generator units 4 adjacent to the switch 12 are connected in parallel between the main lines 5, 6.

The diodes 13 additionally prevent individual

DC

generator units 4 from being short-circuited via one of the main lines 5, 6 and one of the cross-connection lines 11 when the switch 12 is closed.

Switch states of the switches 12 (A to E) are listed in 10 the table below for the circuit stages I to IV shown in Figure 1, a closed switch being represented by and an open switch being represented by Circuit stage/switch A B C D E I 1 1 1 1 1 II 1 1 0 1 1 III 1 0 1 0 1 IV 0 0 0 0 0 Table 1 In circuit stage I, all the switches A to E are closed, with the result that the current flow flows from the negative main line 6 via the first DC generator unit 4.1 via all cross-connection lines 11 and the DC generator units 4.2 to 4.5 as far as the last DC generator unit 4.6 and only there is it conducted into the positive main line 5. All the DC generator units 4.1 to 4.6 are connected in series.

In the second circuit stage II, only the middle switch C is open, as a result of which the DC generator units 4.1 to 4.3 and 4.4 to 4.6 are connected in series and these two units of series-connected DC generator units are connected in parallel between the two main lines 6.

In the third circuit stage III, every second switch

A,

C, E is closed, with the result that the DC generator unit [sic] are connected in series in pairs 4.2) 4.6) and these pairs of DC generator units are connected in parallel between the main lines 6.

n the fourth circuit stage IV, ail the switches ar -Rkh.V a witches are 3p C= :I"

I;V'

11 open, with the result that all the DC generator units 4.1 to 4.6 are connected in parallel with one another.

The control circuit for driving the individual switches has a voltage comparator which measures the voltage UGG generated by a single DC generator unit 4 and outputs, at three digital output channels Kl, K2, K3, the following digital states as a function of the measured voltage

UGG:

K1 K2 K3 Circuit state UGG 6.7 V 1 1 1 I 6.7 V UGG 13.3 V 0 1 1

II

13.3 V UGG 20.0 V 0 0 1 III 20.0 V UGG 0 0 0 Iv Table 2 The voltage ranges specified in Table 2 correspond to the circuit states I to IV, with the result that the digital states of the channels K1 to K3 can be converted into the switching states of the individual switches A to E by a simple logic circuit.

The logic table which must be satisfied by this logic circuit is specified below, the input values being given by Kl, K2 and K3 and the output values being given by the switch states of the switches A to E: K1 K2 K3 A B C D E 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0 1 0 1 1 1 1 0 1 1 1 1 1 1 1 1 1 Table 3 k 12 This results in the following equations for the logic circuit: A K3 B K2 C (KI xor K2) xor K3 D K2 E K4 C can also be represented by NAND gates: C nand K1) nand K2) nand K3) nand 1 In the description of the invention expounded above, DC generator units were in each case connected depending on the voltage requirement. However, for the implementation of the method according to the invention, it is not necessary to provide DC generator units on a generator rather it is also possible for coils of the generator to be directly connected in series, instead of the DC generator units, provided that these coils generate voltages of identical or at least similar phase.

Individual coils are connected in the following description of the invention, it being presupposed that the coils generate voltages of similar phase. It is equally possible for the individual coils to be replaced by DC generator units which respectively encompass any desired coil systems or current sources.

Figure 6 illustrates a further circuit according to the invention, which requires no active switches.

This circuit once again has two main lines 5, C, 13 between which a plurality of branch lines 20.1 to 20.3 extend. Two diodes 21.1 to 21.6 are arranged in each of the branch lines 20.1 to 20.3. Generator coils 22 and 23 are respectively arranged between the branch lines 20.1 to 20.3, a voltage being induced in said generator coils, and said generator coils being connected to the branch lines 20.1 to 20.3 in the regions between the diodes 21.1 to 21.6, the first coil 22 being arranged between the first and second branch lines 20.1, 20.2, and the second coil 23 being arranged between the second and third branch lines 20.2, 20.3. The coils 22 and 23 consequently form a continuous series circuit.

The first coil 22 is formed from a relatively thick wire and has N turns. The second coil 23 has 2N turns and is therefore formed from a somewhat thinner wire.

If the generator is operated, then a respective voltage

U

22

U

23 is induced in the coils 22, 23, 24. Since the voltages are approximately proportional to the number of turns, the following holds true:

U

23 2U22.

If the generator is operated at low rotational speeds, current flows from the main line 6 via the diode 21.2, the first coil 22, the second coil 23 and the diode 21.5 into the main line 5. The partial voltages generated across the coils are added, resulting in a total voltage of UG 3U 22 These current paths apply to the phase in which the coils shown in Figure 6 form a positive pole on the right-hand side and a negative pole on the left-hand side. For the opposite phase, the current paths run via the diode 21.6, the coils 24, 23, 22 and the diode 21.1. Rectification is obtained by this means in a manner known per se. For the purpose of

C'

t z

I-

I II 14 simplification, only the phase which generates a positive pole on the right-hand side of the coils in Figure 6 is considered in the following description of the invention.

If the rotational speed of the generator is increased, then the voltage UG generated by the generator rises and so does the current flowing through the coils.

Since the coil 23 is formed from thinner wire, it is the first to reach its limit current, and that is to say that the current flowing through the coil 23 can no longer be increased.

The voltage collapses to zero volts and the current generated by coil 23 flows via the diode 21.5 onto the main line 5, via the load to the main line 6, via the diode 21.2 to the coil 22 and back into the coil 23.

Since the resultant voltage across the coil 23 is almost zero volts, the resultant power loss can be regarded as negligible. It is calculated as follows: Pv IG dUDiode Ri coil Is 2 where Pv power loss IG coil limit current dUDiode diode differential voltage Ddiode 21.3 Udiode21.5 Ricoil coil internal resistance The method according to the invention is realized by this circuit without an active switch. Active switches are, as a rule, transistors which produce a voltage drop and thus a voltage loss even in the on-state. In the case of this passively operating circuit, only a few resistive components are connected in the current path at low rotational speeds, with the result tha- a maximum output voltage is obtained. The coils i 15 themselves act as switches, the voltage of said coils collapsing after the limit current has been reached.

In principle, this circuit is possible just with two different coils, in which case it is essential that these two different coils form a series circuit at low rotational speeds of the generator with the result that their voltages are added together. For this purpose, it is necessary that the two different coils be connected in series, the ends and the center of the coils being connected to two main lines via two diodes in the manner of a rectifier circuit.

The number of coils can also be increased as desired, it being possible in each case for coils of similar phase or DC generator units to be interconnected in this way.

Figure 7 diagrammatically illustrates a further embodiment of the circuit according to the invention.

It corresponds in its structure to the circuit shown in Figure 6, four coils 31 to 34 being provided, with the result that a total of five branch lines 20.1 to 20.5 with ten diodes 21.1 to 21.10 are necessary. The coils 31, 33 are wound from relatively thick wire and have n and 2n turns. The coils 32, 34 are formed from thinner wire and have 3n and 4n turns. Consequently, in this circuit, coils with a small number of turns and coils with a large number of turns are arranged such that they follow one another alternately. The four coils form a series circuit at low rotational speeds. At higher rotational speeds, the coil 32 with a high number of turns is the first to reach its limit current, with the result that its voltage collapses.

,After the limit current of the coil 32 havic a lrge

N'

1 a a g 16 number of windings has been reached, the coil 31 consequently forms a parallel circuit with the seriesconnected coils 33 and 34, the alternating voltage generated across the coils simultaneously being rectified. If the rotational speed and loading continue to rise, the voltage across coil 34 collapses again in a known manner. Consequently, only the coils 31 and 33 are now connected in parallel and the voltage is again within the desired range.

The circuits illustrated in Figures 6, 7 consequently enable the method according to the invention to be realized without active components.

The method according to the invention has a distinctly higher efficiency compared with generators that are conventionally used, since the output voltage of the generator can be kept in a required voltage range over a wide rotational speed range without appreciable power losses and the generator can output more and more current with a rising rotational speed.

4' i

Claims

1. A generator circuit having generator coils (22, 23; 31, 32, 33, 34) with different numbers of turns, wherein at least two generator coils (22, 23; 31 to 34) are connected in series and two main lines 6) are arranged in parallel with the generator coils, each generator coil being connected to the main lines 6) on both sides via a respective branch line (20.1 to 20.5) and respective diodes (21.1 to 21.10) being oriented identically for a current flow from one main line to the other 1 0 main line after the manner of a rectifier circuit in the branch lines, and each generator coil differing from the or each adjacent generator coil in respect of its limit current resulting from the respective number of turns in such a way that as a result of a rotational speed increase and a resultant voltage rise, the generator coil with the higher number of turns is in each case the first to reach its limit current and, consequently, the voltage across this generator coil o collapses. 0 0%

2. The generator circuit as claimed in claim 1, S.wherein at least three, in particular four, generator coils (31 to 34) are connected in series in such a way that coils (31, 33) with a smaller number of i 20 turns and a higher limit current and coils with a larger number of turns (32, 34) and a smaller limit current are arranged such that they alternate.

3. The generator circuit as claimed in claim 2, wherein a central coil (32) having a relatively smaller limit current is arranged between two outer coils (31, 33) having a higher limit current. I

4. The generator circuit as claimed in claim 3, wherein one of the two outer coils (31, 33) having a higher limit current is adjoined by a further coil (34) in series, the limit current of which lies between the limit currents of the outer coils, on the one hand, and of the central coil, on the other hand. 3 0

5. The generator circuit as claimed in one of claims 1 to 4, wherein the series-connected generator coils (22, 23; 31 to 34) are in each I -18- case coils in which a voltage of identical phase is induced.

6. The generator circuit as claimed in one of claims 1 to wherein the coils with a relatively higher number of turns are wound from relatively thinner wire and the coils with a relatively smaller number of turns are wound from relatively thicker wire.

7. The generator circuit as claimed in one of claims 1 to 6, wherein the generator is designed as a self-excited generator, separately excited generator or as a mixed separately and self-excited generator. 1 0 Dated this 4th day of November 1999 FICHT GMBH CO. KG By their Patent Attorneys COLLISON CO. *o *o **o *o* o*oao N