GB2084767A

GB2084767A - Method and device for feeding loads from a common source

Info

Publication number: GB2084767A
Application number: GB8129470A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1981-09-30
Filing date: 1981-09-30
Publication date: 1982-04-15
Also published as: GB2084767B

Abstract

In a system for feeding loads e.g. vehicle battery and lamps connected to a common voltage source, which have different voltage or current requirements, the arithmetical average value u or peak value and the r.m.s. value U of the supply voltage are regulated differently whilst maintaining the electrical connection between the voltage source and the individual loads. For this purpose, the supply voltage is produced in a pulsed manner, the pulse amplitudes and pulse lengths being regulated individually. An r.m.s. value regulator (1a) determines the magnitude of the output voltage, and an arithmetic average value regulator (1b) determines the relative "on" period of the output voltage. When applied to the electrical system of a motor vehicle fed by a three-phase generator, the r.m.s. value regulator acts upon the field winding of the generator, while the average value regulator triggers thyristors connected to the stator windings with a predetermined frequency and variable duty ratio. <IMAGE>

Description

SPECIFICATION A method and a device for feeding loads from a common source The invention relates to a method and a device for feeding loads connected to a common voltage source.

An object of the invention is to render it possible to supply optional electrically interconnected loads, operating means or the like, connected to a common source of supply voltage with current or voltage values which differ according to the characteristics and requirements of the loads. One particular application of the invention is the power supply of mobile units, particularly motor vehicles, although the invention is not confined to this field of application.

In current generators, in particular in threephase generators in motor vehicles or the like, it it known to influence these generators, despite the high demands made on them, by regulating the excitation current fed to them, such that the output voltage of the generator is maintained at a substantially constant desired level. The excitation current and thus the excitation field in the rotor of the generator are then controlled in dependence upon the voltage generated in the generator, such that the generator terminal voltage remains constant up to the maximum current despite a considerable variation in the rotation speed between idling and full load and despite considerable fluctuations in the load on the generator. Known regulators used for this purpose are the mechanical single-contact or multicontact regulators (Tirrell regulators).Electronic transistorised regulators are now chiefly used and regulate the generator voltage by periodic weakening of the excitation current, usually by switching it on and off periodically, since the voltage generated in the generator is approximately proportional to the product of the rotational speed and excitation current.

Problems can occur in this connection in, for example, the field of motor vehicle electrics in winter or in town traffic, since the internal resistance of the battery also connected to the electrical system increases to a considerable extent at low temperatures, so that the cold starting performance of the battery is reduced to a considerable extent. Moreover, there is a non-compensated battery charging balance. Special charging problems also arise in the case of low rotational speeds.

Although it is possible to impose an adequate charging current even at low temperatures by increasing the charging voltage at least intermittently with a corresponding design of the generator and thus a correspondingly adequate generator output, the voltage of the vehicle electrical system must take voltagesensitive loads into account, such as the incandescent lamps which are used, and thus cannot be increased to an optional extent.

Thus, the present systems constitute a compromise between the requirements of the battery with respect to adequate charging and, for example, the Toads connected to the vehicle electrical system.

Particularly in view of future increasing demands on the quality of the supply voltage in vehicle electrical systems, there is a considerable demand for a central, high-performance regulating system, which, on the one hand, can ensure an adequate battery charging balance and, on the other hand, cannot damage the connected loads, such as reducing their durability.

The present invention resides in a method of feeding loads, connected to a common voltage source, with voltage or current values varying according to the requirements of the loads, in which the electrical connection of the loads to one another and to the common voltage source is maintained whilst the arithmetic average or peak value of the voltage source on the one hand, and the r.m.s. value of the voltage source on the other hand, are regulated and set independently of one another for respectively associated loads.

The invention includes a device for feeding loads, connected to a common voltage source, with voltage or current values differing according to their requirements, comprising a pulse amplitude regulator and a pulse width regulator to which are fed a desired value of the arithmetical average voltage of the peak voltage and a desired value of the r.m.s. voltage, the pulse amplitude regulator and the pulse width regulator acting upon an adjusting means, whereby a pulsed supply voltage is generated having an r.m.s. value suited to one load and an arithmetical average value suited to another load.Thus a battery voltage regulated independently of the vehicle electrical system can be made available when using only one regulator, although only one common vehicle electrical system is provided, and all the loads, including the battery which can also be considered a load when the generator is active, are electrically interconnected. Despite this electrical interconnection, neither the requirements with regard to a constant lamp voltage nor with regard to a variable battery charging voltage need to be abandonned.

It is particularly advantageous to include the three-phase generator in the adjusting means of the regulator in accordance with the invention, such that the peak or arithmetical average value of the supply voltage is adjusted by controlling the field current and, independently thereof, the r.m.s. value is adjusted by controlling the average "on" duration of the generator or the period during which the generator is connected to the vehicle electrical system.

The invention is further described, by way of example, with reference to the drawings, in which: Figure 1 is a graph showing the characteristic of the pulsed output voltage of the system in accordance with the intention, and which at the same time constitutes the supply voltage of the vehicle electrical system; Figure 2 is a block circuit diagram of a first embodiment of a regulator for average and effective regulation; Figure 3 is a block circuit diagram of a second embodiment of a regulating device in which the peak value is regulated instead of regulating the average value; Figures 4a and 4b are respectively a circuit diagram of the vehicle electrical system and a graph of the characteristic of the voltage of the vehicle electrical system and the independent characteristic of the average value and of the effective value of the supply voltage;; Figures 5a and 5b are respectively a circuit diagram showing the correlation of the regulating device, in accordance with the invention, with a vehicle electrical system which is supplied by a three-phase generator, and a graph showing the resultant time function of the vehicle electrical system voltage regulated according to the average and effective value; Figures 6a and 6b are respectively a circuit diagram showing the correlation of the device, in accordance with the invention, with a vehicle electrical system which is supplied by a separate voltage source such as a traction battery, and a graph showing the characteristic of the time function of the voltage of the vehicle electrical system;; Figure 7 is a circuit diagram showing in greater detail, the connection of the threephase generator to the vehicle electrical system by way of controllable semiconductor switches, and Figure 8 is a graph showing the regulating range of the system with the peak voltage and the duty ratio as parameters.

The invention is based on the knowledge that most current supply systems include loads having differing requirements, such as those which require a constant effective value U of the supply voltage, and those which require a specific arithmetical average value u of the supply voltage. When applied to, for example, the electrical system of a motor vehicle, most loads, such as incandescent lamps, require a constant effective value U usually a constant r.m.s. value, of the supply voltage, whereas the battery requires a different arithmetical average value u of the supply voltage according to temperature for optimum charging. Inductive loads, such as servo-motors and the like are also dependent upon the average value u of the supply voltage, although they do not necessarily make special demands on the constancy of the supply voltage.Based on this, the invention proposes to provide a system which renders it possible to adjust the average value and effective value of an optional supply voltage independently of one another within certain limits, so that, on the one hand, the electric interconnection of all the loads connected to the vehicle electrical system can be retained although, on the other hand, each load can be supplied with current and voltage values according to its specific requirements, that is to say, for example, a constant lamp voltage can be ensured at the same time as a variable battery charging voltage in an electrical system of a motor vehicle.

This basic idea can be realised by making the supply voltage a pulsed voltage, such as a train of square-wave pulses as illustrated in Fig. 1. Fig. 1 shows the characteristic of the optional supply voltage u (related to the electrical system of a motor vehicle in the present instance) plotted against time, the amplitude of the individual square-wave pulses at the same time prescribing the peak value û. The relative "on" ratio a is te/T.The following equations result for the average value and the effective value of the supply voltage in the case of a voltage characteristic of this kind which is illustrated in Fig. 1: Average value u = a.u" (1) R.M.S. value U = Na.Q (2) With prescribed values of the effective value U and of the average value ii, one obtains the necessary adjusting quantities from these formulae as follows: u2 (3) U2 and U2 (4) u Thus, the relative "on" period a increases with u; the peak value of the supply voltage ú increases with the r.m.s. value U. This is the basis of the function of the regulator, in accordance with the invention, which is illustrated in greater detail in Fig. 2. The regulator illustrated in Fig. 2 is constructed such that, to enable different adjustment of the r.m.s.

value U and of the arithmetical average value u of the supply voltage u, the pulse amplitude, that is to say, the peak value û and the relative "on" period a are subjected to regulation dependent upon the desired r.m.s. value and average value. For this purpose, the overall regulator includes a regulation portion 1, an adjusting portion 2 and a measuring and feedback portion 3, as well as separate circuits 4 and 5 for providing the desired value of the r.m.s. value U (herein the form of Us2) and the arithmetical average value u. The regulating portion 1 includes a first component regulator or r.m.s. value regulator 1 a which controls the peak value û, and a second component regulator or average value regulator 1 b which determines the relative "on" period a.The two regulators 1 a and 1 b are proportional plus integral regulators (PI regulators). The output of the r.m.s. value regulator 1 a is fed by way of a coupling component 6 having a coupling factor K1 to a summation circuit 7 and then to a switch 8, preferably an electronic switch, whose switching function plotted against time (relative "on" period a) is controlled by a two-state switch 9 having a defined threshold value, such as a Schmitt trigger. The peak value, pulsed in this manner by the switch 8, is applied as a supply voltage u to the vehicle electrical system by way of an amplifier 1 0.

The output of the second component regulator or average value regulator 1 b is connected by way of a further coupling component 11 having a coupling factor K4, a further summation point 8' and to a summation point 1 2 connected in series therewith to the input of the Schmitt trigger 9. The frequency of the pulsed supply voltage is determined by a freerunning generator such as a saw-tooth generator 1 3 whose saw-tooth voltage (its characteristic is indicated in the circuit block of Fig. 2) is compared with the output of the average value regulator 1 b at the summation point 1 2.

The summation point 1 2 and the Schmitt trigger 9 could be combined to form an "adding Schmitt trigger".

The actual values for the r.m.s. value and the average value are obtained from the supply voltage u by way of a feedback connection lead 14 and are applied as average value u by way of a first low-pass filter 1 5 to a summation point 1 6 which is located on the input side of the average value regulator 1 b at which the average value actual voltage u is compared with the average value desired voltage us originating from the circuit 5.The square of the r.m.s. value is obtained by feeding the supply voltage uto a squaring circuit 1 7 whose output is also connected to a low-pass filter 1 8. The comparison of the squared actual r.m.s. value U2 (this is easier to realise electronically than the r.m.s. value U) with the squared desired r.m.s. value U2s, which is fed from the desired value setter 4, is effected at the summation point 1 9. The control circuits can be decoupled at the operating point by way of coupling components 20 and 21, each of which coupling components acts upon a respective one of the summation points 7 and 8 connected on the output side from the output of the respective other regulator. This will be further discussed below.However, in the first instance, it will be assumed that the coupling factor K2 of the cross-coupling component 20 and the coupling factor K3 of the cross-coupling component 21 are zero in each case.

The following function then ensues. The r.m.s. value regulates the pulse amplitude and, in the embodiment illustrated in Fig. 2, also itself produces, as its own adjusting member so to speak, the peak value û of the pulsed output voltge u. The average value regulator completes the control principle by pulse length regulation which acts in combination with the pulse amplitude regulation, and specifies the relative "on" period a.

Since the two regulators 1 a and 1 b have integrating parts, the control errors AU2 and Au decay to zero. Thus, any possible nonlinearities in the equations (1), (2), which are caused by the multiplicatively acting adjusting portion 2, are completely stabilised. The freerunning saw-tooth generator 1 3 acts in a frequency-determining manner.The magnitude of the analog output signal a' of the average value regulator 1 b present at the input of the adding Schmitt trigger 9, 1 2 and the rise in the saw-tooth generator signal varying with respect to time, results in the "on-off" ratio at the Schmitt trigger 9 and thus a square-wave output voltage whose relative "on" duration a determines the relative "on" duration of the electronic switch 8, and thus the average value of the supply voltage u at the output of the amplifier 1 0. The electronic switch 8 therefore realises the time function illustrated in Fig. 1.The measuring components 1 5 and 1 7 and 18 in the feedback portion 3 determine the average value u and the squared r.m.s. value U2 from the time function u and makes these values available at the regulator inputs for comparison with the desired values.

The two regulating circuits for r.m.s. value and average value interact by way of the adjusting portion 2. By way of example, if the desired value of squared r.m.s. value U2s varies, the peak voltage û is adjusted in the first instance; u and U then follow with a delay by way of the feedback measuring components 15, 1 7, 18. The average value regulator 1 b then also detects a difference and varies a, namely by varying the analog output voltage a'. The comparison of the desired and actual values at the effective value regulator 1 a is thereby again influenced, and so on. Thus, conditioned by the system, a stabilizing time results which is relatively long compared with the cut-off frequency of the measuring component.

If the circuit illustrated in the form of a block circuit diagram in Fig. 2 is used to regulate the voltage of the electrical system in a motor vehicle or the like, the desired values produced by the desired value setters 4 and 5 can be variable, as is otherwise usual, this being necessary particularly for the desired value of the average value u5 responsible for charging the battery. Thus, the desired value of the average value can be additionally correspondingly influenced by feeding the actual battery voltage UB, the battery charging cur rent 1, and the battery temperaturet. The regulating range realised by the invention, or the regulating range required for a vehicle electrical system, will be further described below with reference to Fig. 8.

In the case of a limited regulating range, the two regulating circuits for the average value and the r.m.s. value can also be linearised about the operating point which should lie approximately in the centre of the range.

Thus, with suitble choice of the coupling factors K1, K2, K3 and K4 of the coupling components 6, 11, 20, 21 the regulating circuits can be decoupled at the operating point. The equations (3) and (4) given above show that U2 acts negatively upon a, and u acts negatively upon ir. The cross-couplings by way of the components 20 and 21 are thus negative, as is also indicated at the summation points 7 and 8. The negative couplings lead to monotonic instability for points outside the regulating range illustrated in Fig. 8; on the other hand, the regulating dynamics are distinctly improved for points within the range.

In a variant as illustrated in Fig. 3, it is alternatively possible to regulate the peak value and r.m.s. value of the voltage instead of regulating the average value and the r.m.s.

value. The corresponding circuit is shown in Fig. 3 in which the reference numerals of circuit portions operating in the same manner as corresponding circuit portions in Fig. 2 are provided with an apostrophe; identical circuit components are provided with the same reference numerals. In the embodiment of Fig. 3, the pulse width regulator la' regulates the peak value and the pulse length regulator 1 b' regulates the r.m.s. value. The desired r.m.s.

value setter 4 and the low pass filter 18 in the corresponding feedback circuit are thus connected to the summation point 1 6 at the input to the pulse length regulator 1 b'.

In order to produce the actual value of the peak voltage Q, a circuit is provided which produces this peak value and which, in the embodiment of Fig. 3, is constituted by a "sample and hold" circuit 22, which is connected to the summation point 1 9 at the input to the pulse width regulator 1 a'. This "sample and hold" circuit 22 is kept in phase by the Schmitt trigger 9 which produces the relative "on" period a and which is connected in parallel with the switch 8. A desired peak value setter 23 is provided instead of the desired average value setter 5 and is connected to the summation point 1 9. In this connection, it may be pointed out that the desired value setters can be resistor-divider circuits in a practical construction.In the case of a variable desired value, function generators, known per se, can be provided which, in conformity with varying input data of UB, 1B and eMBf produce a varying desired output value. The PI regulators are known per se, and also the construction of low-pass filters.

The coupling components can also be resistor divider circuits, so that there is no need to discuss the block circuit diagrams in detail.

Referring to the embodiment of Fig. 3, it may be mentioned that only a variation in the peak value regulating circuit 1 a' affects the regulation of the r.m.s. value but not vice versa, so that, in the embodiment of Fig. 3, only one coupling component 24, which acts with a coupling factor K at the summation point 25 from the output of the PI regulator 1 a' for the peak value is needed. A cross coupling is only required from the peak value regulating circuit to the r.m.s. value regulating circuit. All the other elements of the construc tion, and the function, are the same as those already described with reference to Fig. 2.

A simulation of a vehicle electrical system having a battery 26, lamps 27 and servo motors 28 is illustrated in the manner of a demonstration circuit in Fig. 4a. The lamps 27 and the servo motors 28 are connected directly to the lead which carries the supply voltage u (6) and which originates from the regulator 29 in accordance with the invention.

The battery 26 is connected to the lead by way of a switch 30 and a diode 31 which is reverse-biassed with respect to the flow of current from the battery to the supply lead. A controllable semiconductor switch, preferably a thyristor 32, is connected in parallel with the blocking diode 31 and has a firing circuit comprising a push-button 33 and a series resistor 34. Measurments made on the circuit of Fig. 4a have shown that, when the battery is isolated (switch 30 open), the brightness of the lamps 27 and the rotational speed of the motor 28 can be adjusted virtually indepen dently of one another by corresponding ad justment of the desired magnitudes of the r.m.s. values and of the average values by the regulator 29, as already discussed above.This regulating capability is maintained to a consid erable extent even when the battery is con nected, the diode 31 preventing discharge of the battery during the pulse intervals and enabling the average value UB of the battery voltage directly on the battery terminals to be higher than the effective value U on the output terminals of the regulator 29 (see also the illustration of Fig. 4b). Referring to Fig.

4b, the pulsed square-wave supply voltage u (t) is shown by a thin solid line, the battery voltage UB (t) varying with respect to time is shown by a broken line, and the average battery voltage UB is shown by a dash-dot line. If the performance of the regulator 29 is inadequate (if, for example, a corresponding three-phase generator is not driven when a motor vehicle engine is not running), voltage is supplied from the battery by pressing the push-button 33 and firing the thyristor 32.

The thyristor is automatically switched off when the regulator performance is adequate (Û SIJB) A distinction can be made between two cases of practical application when the regulator in accordance with the invention is used for vehicle electrical system, that is to say, on the one hand, feeding the battery and the electrical system from a three-phase generator as is done in motor vehicles having internal combustion engines and which is shown diagrammatically in Fig. 5a with corresponding adaptation of the regulator in accordance with the invention and, on the other hand, feeding the battery and the electrical system from a larger voltage source such as a d.c. voltage source in the form of a traction battery, for example in a motor vehicle which is driven by an electric motor and in which energy is stored by way of a corresponding battery block.

Referring to Fig. 5a, in which the battery 26' and the positive lead 35 of the vehicle electrical system are fed by a generator which is a three-phase generator 36, the adaptation and correlation are such that the excitation current If of the field winding 36' of the threephase generator is controlled by a peak value regulator la" which thus determines the value of the voltage supplied by the three-phase generator, while the r.m.s. value regulator 1 b" determines the average "on" period or the average period during which the threephase generator is connected to the electrical system lead 35.In this case, the peak value regulator la" can also be designated "battery regulator", since it acts according to the requirements of the battery and is also fed with a battery temperature signal (9 by way of at least one further connection lead 37 coming from the battery. Thus, the peak voltage û which the battery regulator 1 a" feeds to the excitation winding 36' in order to produce a correspondingly proportional excitation current, is a function of the battery temperature.

The signal a of the average "on" period is fed from the r.m.s. value regulator 1b" to an electronic switch 38 which is preferably a controllable electronic semiconductor switching element and, in the practical application illustrated in Fig. 7, comprises three positive thyristors 38a and three negative thyristors 38b in a full-wave rectifier diode bridge configuration for three-phase generators. A special simplification in this case of correlation, is that it is only necessary to use the thyristors 38a, 38b to replace the diodes which, in any case, are provided in any three-phase genertor, all six thyristors 38a, 38b being simultaneously fired by the average value regulator 1 b", and those biassed in the forward direction being switched on.Each of the pulse trains thus produced then still has a certain residual ripple which originates from the sinusodial phase voltages in the stator windings u, V, w of the three-phase generator. As in the embodiment of Fig. 4a for example, the battery 26' in the embodiment of Fig. 5a is connected by way of a thyristor 32' and a diode 31' connected in antiparallel therewith, wherein the current path through the diode 31' can also be choked by an inductance 39 in order to avoid high charging current peaks.

The other loads are represented in their entirety by the resistor 40. A free-running circuit comprising a further inductance 41 and a free-running diode 42, can also be provided for conducting transients in order to increase the performance, so that a predetermined flow of current from the inductance to earth by way of the free-running diode 42 can still be maintained during the pulse intervals. When the limiting current of the excitation is reched, the peak value regulator 1 a" additionally fires the thyristor 32' during the pulse intervals by way of the connection lead 43, so that the battery 26' can act as a buffer. The characteristic of a supply voltage of this kind is shown in Fig. 5b.

In the embodiment of application shown in Fig. 6a, that is to say, feeding the battery and -electrical system from a traction battery 44 by way of a charger constructed in accordance with the invention, the construction and function of the circuit elements in the plane of the drawing on the right of the dash-dot line 45 are the same as those in the embodiment of Fig. 5a, so that they will not be further discussed. In the present instance, the regulation according to peak value and r.m.s. value is effected by the series combination of two switching functions which act upon a main contact breaker switch 46 and which determine the two relative "on" periods a and b.

Thus, the peak value regulator 1 a" specifies a relative "on" ratio b for a higher frequency pulse train which is produced in the circuit 47, which ratio is determined by the ratio of the peak voltage û to the battery voltage UB1 of the traction or main battery 44. As shown in Fig. 6b, in the time characteristic of the electrical system voltage u, (t) before the freerunning circuit comprising inductance 41 and diode 42, the relative "on" ratio b specified by the peak value regulator 1a" is fixed at t2/T2. The higher frequency of the switching function originating from the relative "on" ratio b lies at at least approximately 500 Hz or can be set to this value. Thus, the relative "on" period b determines the mean arithmetical value tr,(t) which corresponds to the regulating voltage û. A control pulse train of lower frequency, originating from the r.m.s. value setter 1 b" and which lies at approximately 50 Hz, results in a double modulation by way of a switch function circuit 58, the final effect of this being the yielding of high-frequency square-wave pulses of the period T2 as shown by the time function characteristic of Fig. 6b, to form the pulse trains which in turn have the relative "on" period of a= t,/T,. The formation of the pulse trains having the rela tive "on" period a is determined by the r.m.s.

value regulator. The time function of the electrical system voltage u (t), which is shown by solid lines in Fig. 6b, is then obtained beyond the inductance 41, and is made accessible to the loads and the battery. The r.m.s. value and peak value of the system voltage u/t are regulated separately from one another in conformity with the requirements of the battery and other loads.

Finally, the possible variation of the r.m.s.

voltage U plotted against the arithmetical average voltage u within the meaningful regulating range is illustrated in the graph of Fig. 8, the relative "on" ratio a and the peak voltage u being specified as parameters. The limitations O < a < 1 (5) and O%uU%û (6) generally apply.

The peak voltage is limited to 35 V for, for example, technical reasons connected with the equipment. It will be seen that a considerable regulating range can be obtained within the ranged specified by the curve of û = 35 V and a = 1.0, the limited regulating range, constituted by the rhombus-like rectangle having a periphery marked by dashes, applying in the case of the regulator circuit decoupling mentioned above. The regulating range necessary for a 14 V electrical system is indicated by the narrow horizontal bars within this limited regulating range. Within this again limited regulating range, the separate influencing of the battery charging balance on the one hand and the other electrical system loads on the other hand can be reliably effected with respect to regulating technology.

All the features set forth in the description and in the claims, and illustrated in the drawings, can be material to the invention individually and in any optional combination with one another.

Claims

1. A method of feeding loads, connected to a common voltage source, with voltage or current values varying according to the requirements of the loads, in which the electrical connection of the loads to one another and to the common voltage source is maintained whilst the arithmetric average or peak value of the voltage source on the one hand, and the r.m.s. value of the voltage source on the other hand, are regulated and set independently of one another for respectively associated loads.

2. A method as claimed in claim 1, in which a pulsed supply voltage is generated and its value and its relative "on" time are separately varied.

3. A method as claimed in claim 2, in which a pulse amplitude modulation of the supply voltage is combined with a pulse length modulation, a desired value dependent upon the desired r.m.s. value of the supply voltage being specified for the pulse amplitude, and a desired value dependent upon the desired arithmetical average value is specified for the pulse length.

4. A method as claimed in claim 2, in which a pulse amplitude modulation of the supply voltage is combined with a pulse length modulation, a desired value dependent on a desired peak value being specified for the pulse amplitude, and a desired value dependent upon the desired r.m.s. value is specified for the pulse length.

5. A device for feeding loads, connected to a common voltage source, with voltage or current values differing according to their requirements, comprising a pulse amplitude regulator and a pulse width regulator to which are fed a desired value of the arithmetrical average voltage or the peak voltage and a desired value of the r.m.s. voltage, the pulse amplitude regulator and the pulse width regulator acting upon an adjusting means, whereby a pulsed supply voltage is generated having an r.m.s. value suited to one load and an arithmetrical average value suited to another load.

6. A device as claimed in claim 5, in which the pulse amplitude regulator comprises a PI regulator and its input is fed with a difference between the desired value and a feedback actual value.

7. A device as claimed in claim 6, in which the output of the pulse amplitude regulator is fed to a switch whose relative "on" period determining the pulse width is controlled by the output of the pulse width regulator.

8. A drvice as claimed in claim 5, 6 or 7 in which the pulse width regulator comprises a PI regulator and its input is fed with the difference betwen the desired value and a feedback actual value.

9. A device as claimed in claim 8, in which the output of the pulse width regulator is fed as an analogously varying voltage to a comparator whose other input is connected to a monotonically rising voltage, and a two-state switch is connected to the output side of the comparator such that the two-state switch is switched over when a predetermined value is reached.

10. A device as claimed in claim 9, in which the comparator is an adding Schmitt trigger and the output of the pulse width regulator is connected to the input of the Schmitt trigger to which the output signal of a saw-tooth generator is additionally fed, such that there is produced at the output of the Schmitt trigger a square-wave switching voltage having a relative "on" period ratio for operating the two-state switch.

11. A device as claimed in claim 10, in which an amplifier is connected to the output of the two-state switch r.m.s. which determines the relative "on" period, and in which the output supply voltage is fed back by way of low-pass filters to comparators in the input circuits of the r.m.s. value and arithmetrical average value regulators.

1 2. A device as claimed in any of claims 8 to 11 when appendent to claim 6 or 7, in which at least one cross-coupling component is provided between the outputs of the PI regulators, such that the regulators are decoupled at one point of operation.

1 3. A device as claimed in any of claims 5 to 12, in which the pulse amplitude regulator is arranged to regulate the value of the r.m.s. voltage and the pulse width regulator is arranged to regulate the value of the arithmetical average voltage.

14. A device as claimed in any of claims 5 to 12, in which the pulse amplitude regulator is arranged to regulate the value of the peak voltage and the pulse width regulator is arranged to regulate the value of the r.m.s.

voltage.

1 5. A device as claimed in claim 1 3 or 14, in which a squaring component is provided in the feedback circuit to the r.m.s.

value regulator, such that the square of the actual r.m.s. voltage is compared with the square of the desired r.m.s. voltage.

16. A device as claimed in claims 10 and 1 4 or in claim 1 5 when dependent fom claims 10 and 14 in which a sample and hold circuit is connected to the output voltage and is adapted to be switched by the Schmitt trigger in synchronism with the two-state switch.

1 7. A device as claimed in claim 7 or in any of claims 8 to 1 6 dependent from claim 7, which is used with a vehicle electrical system supplied by a three-phase generator, and in which the output of the pulse amplitude regulator is connected to the excitation winding of the three-phase generator, and the said switch determining the pulse width is disposed in a connection lead between the three-phase generator and the vehicle electrical system.

18. A device as claimed in claim 17, in which the said switch determining the pulse width comprises controllable semiconductors also serving as rectifier diodes for the output of the three-phase generator, and in which a battery is connected to the thyristors by way of a diode for charging the battery from the vehicle electrical system and for supplying power to the vehicle electrical system by way of a controllable semiconductor switch which is fired by the pulse amplitude regulator in the pulse intervals upon attaining a limiting excitation current.

1 9. A device as claimed in claim 1 7 or 18, in which a free-running circuit comprising a series inductance and a parallel free-running diode is provided for improving the performance and connects the three-phase geneator to the vehicle electrical system.

20. A device as claimed in claim 7 or in any of claims 8 to 1 6 when dependent from claim 7, which is used with a vehicle electrical system supplied by a traction battery and in which the pulse amplitude regulator and the pulse width regulator produce switching frequencies of which one is modulated by the other, the mutually modulated frequencies controlling the said switch determining the pulse width, such that a series of pulse trains which are separated at intervals are produced and are applied to a free-running circuit comprising a series inductance and a parallel freerunning diode to provide a vehicle electrical system supply voltage.

21. A device as claimed in claim 20, in which a circuit is provided to produce from the output of the pulse amplitude regulator a first control frequency which is conducted by way of a further switch whose switching on and off is determined by the pulse width regulator to control the output switching of the said switch by which the traction battery is connected to the vehicle electrical system.

22. a device as claimed in any of claims 7 to 21, in which the or each switch is an electronic switch.

23. A method of feeding loads substantially as herein described with reference to the drawings.

24. A device for feeding loads constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.