GB2124805A

GB2124805A - Voltage regulators for permanent magnet excited generators

Info

Publication number: GB2124805A
Application number: GB08311397A
Authority: GB
Inventors: Edgar Kuhn
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1982-07-15
Filing date: 1983-04-27
Publication date: 1984-02-22
Also published as: DE3226426A1; JPS5928845A; GB2124805B; GB8311397D0

Abstract

A voltage regulator for a permanent magnet excited a.c. generator, particularly a three-phase generators on a motor vehicle, has a semiconductor rectifier assembly containing controllable rectifiers (thyristors) (15, 16, 17), whose control electrodes are connected to a control transistor (T) through a control capacitor (C) which is connected to the load resistor (29) of the control transistor (T). The transistor (T) is responsive to oscillation of a multi- vibrator (MV) whose operation is dependent upon the voltage of the d.c. system fed by the rectifier assembly in relation to a desired value. <IMAGE>

Description

SPECIFICATION Improvements in or relating to voltage regulators for permanent magnet excited generators The present invention relates to voltage regulators for permanent magnet excited generators.

German Auslegeschrift 1 538 320 discloses a voltage regulator for a permanent magnet excited multi-phase a.c. generator, in which a blocking oscillator includes a transformer having a first winding located in the collector circuit of a transistor, a feedback winding connected to the base of the said transistor, and a third winding which is connected to the control electrodes of controllable rectifiers and renders the latter conductive for as long as the voltage of the d.c. system remains below a predetermined desired value. As soon as the voltage of the d.c. system reaches or exceeds this desired value, oscillations of the blocking oscillator cease, so that the rectifiers can no longer become conductive.

It is necessary to seal the blocking oscillator and the associated transformer in an air-type manner for operation on vehicles, the sealing compound used having to ensure mechanical resistance to vibration particularly when these parts are built into the generator. Furthermore, the blocking oscillator requires a housing having a suitably large volume.

According to the present invention there is provided a voltage regulator for a permanent magnet excited multi-phase a.c. generator having connected to its output side a rectifier assembly which contains controllable rectifiers (thyristors) for feeding a d.c. system, in which the control electrodes of the controllable rectifiers are connected to a control transistor which is controlled from its conductive to its non-conductive state in rhythm with the oscillations of a multivibrator the commencement and termination of whose oscillations are dependent upon the prevailing value of the voltage of the d.c. system as determined by a measuring member such as a Zener diode, and in which a control capacitor is disposed between the control transistor and the control electrodes and is charged by the control transistor, the controllable rectifiers being brought into their conductive states by the discharge current of the control capacitor.

A regulator for a multi-phase a.c. generator suitable for operation on motor vehicles and embodying the present invention can have very small spatial requirements and can ensure long durability.

The invention will be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a basic circuit diagram of one embodiment of the invention, and Figure 2 is a diagram showing some details of the circuit diagram of Fig. 1.

Referring to Fig. 1, a permanent magnet excited three-phase generator 10 has three star-connected phase windings 11, 1 2 and 1 3 which are staggered electrically by 120 relative to one another and in which a voltage is induced by a rotor which is indicated at 1 4 and which is equipped with permanent magnets.

Each of the phase windings is connected to an anode of one of three controllable rectifiers (thyristors) 15, 16, 1 7 and to a cathode of a rectifier 21, 22 and 23. The anodes of the rectifiers 21 to 23 are interconnected and are connected to a negative lead 26, while the cathodes of the controllable rectifiers 1 5 to 1 7 are interconnected and connected to a common positive lead 27. The two leads 26 and 27 form part of a d.c. electrical system of a motor vehicle (not illustrated) whose starter battery is indicated at 28 and is to be kept at a substantially constant state of charge irrespective of the prevailing power requirement of the loads or power consuming devices of the vehicle, so that a constant direct voltage can be made available for these loads.

A voltage regulator embodying the present invention, is provided for this purpose and is hereinafter described. The controllable rectifiers 1 5 to 17, which can be conductive only during the positive half-waves of the induced alternating voltages and can then supply charging current to the battery, are controlled by a control transistor T which is connected to a multivibrator MV indicated by broken lines.

The oscillation frequency of this multivibrator is chosen so as to be a multiple of the generator frequency occurring at maximum drive speeds. The multivibrator is controlled in dependence upon the direct voltage prevailing between the leads 26 and 27, such that the multivibrator oscillates for as long as the desired value of the direct voltage has not been reached, and ceases to oscillate as soon as the desired value is reached or exceeded.

In order that the control oscillations produced by the multivibrator MV can be transmitted to the control electrodes 18, 19, 20 of the rectifiers 15, 16 and 1 7 in a simple manner, a capacitor C is connected to load resistor 29 of the control transistor T. The load resistor 29 is connected to the positive lead 27, and the capacitor C is connected by way of a limiting resistor 25 to the interconnected control electrodes of the rectifiers 1 5 to 1 7. The capacitor C is charged with the polarity shown in Fig. 1 when the transistor T is conducting, and, when the transistor T is non-conducting, the capacitor C discharges by way of the gate to cathode paths of the controllable rectifiers 1 5 to 1 7 which are thereby fired. The battery 28 is then charged.

The multi-vibrator MV is switched off when the battery voltage exceeds the desired value determined by the two voltage divider resis tors 30, 31 and the breakdown voltage of the Zener diode Z. The Zener diode Z becomes conductive when the desired value is exceeded, and the controllable rectifiers can no longer assume a conductive state. The purpose of the diode D is to decouple the capacitor C from the battery voltage during the discharge operation, so that the discharge current of the capacitor can flow through the controllable rectifiers 14 to 1 7.

The special advantage of the use, in accordance with the invention, of the capacitor C resides in the fact that there is no need to provide a hitherto conventional blocking oscillator and, owing to the small dimensions of the capacitor, a smaller governor housing can be provided. A specific firing energy is required which is chiefly determined by the magnitude of the capacitor C. Compared with a blocking oscillator, the capacitor C is advantageous with respect to cost, also in view of the fact that, owing to the high vibratory stress, the blocking oscillator would additionally have to be sealed with a sealing compound when it is to be built into a generator.

Fig. 2 shows one of the possible embodiments of the astable multivibrator MV. The parts in Fig. 2 which are the same as, or which act in the same way as, the parts in Fig. 1 are provided with the same reference numerals as in Fig. 1.

The multivibrator MV bordered by broken lines includes two transistors T1 and T2 which are complementary to one another, the emitter of the p-n-p transistor T1 being connected to a control lead 33 which is connected to the positive lead 27 by way of an ignition switch ZS for the purpose of controlling the operation of the motor vehicle. These two transistors are interconnected by way of a feedback circuit in which a series combination comprising a resistor R1 and a feedback capacitor C1 is connected between the collector of the transistor T1 and the base of the transistor T2.The base of the control transistor T is connected to the collector of the transistor T1 by way of a resistor R3, while the base current required for the oscillations to be produced is supplied to the base of the transistor T2 by way of a resistor R2 for as long as the direct voltage of the vehicle electrical system prevailing between the negative lead 26 and the positive lead 27 lies below the desired value determined by the voltage divider resistors 30, 31 and the breakdown voltage of the Zener diode Z.The dependence upon the prevailing value of the direct output voltage of the generator is obtained by a switching transistor T4 whose emitter-collector path is connected in parallel with the baseemitter path of the transistor T2 and shortcircuits the base-emitter path of the transistor T2 as soon as the voltage on the tapping of the voltage divider 30, 31 exceeds the breakdown voltage of the Zener diode Z and the base-emitter path of the transistor T4. During operation, the emitter of the transistor T4 is permanently biased to the Zener voltage of the Zener diode Z.

In contrast to the arrangement of Fig. 1, the Zener diode Z in the circuit of Fig. 2 is connected to the negative lead 26 and, by way of a resistor 34, to the control lead 33, and directly to the two emitters of the transistors T2 and T4.

As indicated above, the rectifiers 15, 1 6 and 1 7 can be controlled into their conductive states by the control transistor T upon each oscillation produced by the multivibrator MV, provided that the direct voltage of the vehicle electrical system remains below the predetermined desired value. However, when this desired value is reached, the switching transistor T4 short-circuits the transistor T2, so that oscillation can no longer be produced and the rectifiers 15, 1 6 and 1 7 remain in their nonconductive states.

Claims

1. A voltage regulator for a permanent magnet excited multi-phase a.c. generator having connected to its output side a rectifier assembly which contains controllable rectifiers (thyristors) for feeding a d.c. system, in which the control electrodes of the controllable rectifiers are connected to a control transistor which is controlled from its conductive to its non-conductive state in rhythms with the oscillations of a multivibrator the commencement and termination of whose oscillations are dependent upon the prevailing value of the voltage of the d.c. system as determined by a measuring member such as a Zener diode and in which a control capacitor is disposed between the control transistor and the control electrodes and is charged by the control transistor, the controllable rectifiers being brought into their conductive states by the discharge current of the control capacitor.

2. A device as claimed in claim 1, in which the control capacitor is connected to the collector of the control transistor and to a resistor which together with a diode, is connected to one of the two main leads of the d.c. system, and the second electrode of the diode is connected to the capacitor and to the control electrodes.

3. A voltage regulator for a permanent magnet excited multi-phase A.C. generator, constructed and arranged and adapted to operate substantially as herein particularly described with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.