Method of operating a load from alternating current mains and circuit arrangement therefor

In the disclosed circuit arrangement for operating the load from alternating current lines, an inductance connected to the load serves as a first energy store. A first control switch switches the energy storage on and off in response to a regulator circuit. A second control switch connected across the inductor and a series current sensor responds to the control circuit to supply current to the load through a diode which prevents current from flowing directly from the power lines.

BACKGROUND OF THE INVENTION 
The invention relates to a method of operating a load from alternating 
current mains, wherein a quantity of energy is withdrawn from the AC 
current mains in single short switch intervals, is stored temporarily 
and/or supplied to the load, and wherein each half wave in the AC mains is 
subdivided into a plurality of switch intervals. In each of these 
intervals, a cycle elapses during which energy is withdrawn from the AC 
mains, and using simultaneous intermediate storage, a quantity of energy 
is delivered to a final store and/or to the load, or vice versa. 
For carrying out this known method, use is made mainly of so-called "high 
set regulators" which are composed of a rectifier circuit, a switch which 
effects turning on-and-off an inductor that serves as an intermediate 
store to or from the rectifier circuit, and which is controlled by a 
regulator circuit, and a capacitor which serves as a final store. Hence, a 
small quantity of energy is taken from the supply mains in single short 
switch intervals, is stored temporarily as current in the inductor, and is 
stored in the capacitor, until it is used up in the load. In this manner, 
the voltage level is converted from the actual value of the supply mains 
voltage to the approximately constant voltage value of the storage 
capacitor. 
The regulator circuit forces an approximately sinusoidal variation of the 
mean value of the current taken from the supply mains. However, in this 
case, the direct voltage applied to the load is not constant, but exhibits 
a waviness whose magnitude depends upon the source frequency, the current 
carried by the load, the load voltage and the magnitude of the storage 
capacitance. 
This makes it possible for the reaction of the operation of a load with 
rectified alternating current to the alternating current supply mains, 
particularly the occurrence of harmonics which interfere with other loads, 
to be kept low. However, it does result in a decisive disadvantage, namely 
a substantial waviness of the direct current applied to the load or, in 
order to keep this waviness within limits, the need for very expensive 
structural components, particularly the storage capacitor. Also, the 
storage capacitor causes considerable problems because of its large volume 
and, if it has to be constructed as an electrolytic capacitor, its limited 
service life. 
SUMMARY OF THE INVENTION 
It is the object of the invention to avoid these disadvantages and to 
propose a method of the above-mentioned type, which, on the one hand, 
ensures a sinusoidal variation of the current taken from the alternating 
current supply mains and a very small waviness of the direct voltage 
applied to the load, even when small capacitances serve as final stores. 
In accordance with the invention, this is ensured by essentially adjusting 
the current averaged over an entire switch interval and taken from the AC 
mains during the energy withdrawal to the current value suitable for 
maintaining a sinusoidal variation of the mains current during the switch 
interval. 
In a further feature of the method according to the invention, during each 
cycle elapsing in the switch intervals, a residual amount of the 
temporarily stored quantity of energy is maintained when the delivery of 
energy to the final store and/or to the load is interrupted. It is 
particularly advantageous to take the quantity of energy from the 
rectified AC mains. 
In this manner, the withdrawal of current from the AC mains adapted to the 
sinusoidal variation of the current taken from the mains results in an 
extremely slight reaction of the rectification on the mains. In addition, 
supplying very small quantities of energy to the final store in very short 
intervals, ensures a constant voltage at the fiinal store, and thus, the 
voltage applied to the load, even if the final store has only a small 
capacitance. This is because the quantities of energy transported are 
small. In addition, when the final store has very small capacitance values 
or is not present at all such as in the case of loads having small 
capacitances due to their structural designs, for example, winding 
capacitances, the voltage of the final store remains practically unchanged 
by the supply of such a small quantity of energy during a switch interval 
and, on the other hand, these quantities of energy are supplied in such 
short intervals that the supply could be called quasicontinuous. In the 
method according to the invention, a final store may not even be required 
when the load has sufficient integrating properties. 
Another object of the invention is to provide a circuit arrangement for 
carrying out the method according to the invention. 
In a circuit arrangement having an inductor serving as intermediate store 
and connected to a final store and/or to the load, and having at least one 
switch controlled by a regulator circuit for connecting and disconnecting 
the intermediate store, this object is met in accordance with the 
invention by providing a further switch which is connected to the 
regulator circuit and is connected in parallel to a series connection 
composed of the inductor and a current sensor whose signal output is 
connected to the regulator circuit, and by making it possible that this 
series connection can be connected to the AC mains over one or more 
switches controlled by the regulator circuit. 
This measure assures that the load, or device serving as final store, is 
never supplied directly by the AC mains, but only by the intermediate 
store formed by an inductor, and, thus, the final store is not subjected 
to voltage variations. The switch provided in addition to the series 
connection which includes the current sensor and the inductor, make it 
possible to maintain a phase in the cycle of a switch interval during 
which current is neither taken from the mains nor is current supplied to 
the load, and only the residual energy remaining in the inductor is 
practically maintained, while the attentuation caused by unavoidable ohmic 
losses remains negligible when this circuit is appropriately dimensioned. 
This makes it possible in a very simple manner to bring the mean value of 
the current taken from the mains during a switch interval to exactly that 
level which is required for insuring that the variation of the current 
supplied to the arrangement is sinusoidal and in phase with the voltage. 
According to another feature of the invention, the series connection 
including the inductor and the current sensor is connected via a diode to 
the load and/or the final store. This diode prevents the direct flow of 
current from the AC mains to the load and/or to the final store. 
Furthermore, a rectifier circuit can be provided. The latter can be 
connected via a controlled switch to the inductor serving as the 
intermediate store. 
In accordance with another feature of the invention, the switch that 
optionally connects the series connection to the rectifier circuit is 
controlled by a pulse width modulator circuit whose input is connected to 
a desired value generator for the mains current, preferably a voltage 
divider connected to the mains, and which is connected to the current 
sensor over an analog gate circuit and an averaging unit connected to the 
latter. 
This measure ensures a pre-processing of the mains current by the signal 
utilization in the analog gate circuit and the series-connected averaging 
unit for obtaining a sinusoidal variation, the analog gate circuit making 
it possible for the acutal value of the mains current to be picked up only 
during the first phase of a switch interval during which the intermediate 
store is being charged. This further ensured that the time during which 
the switch effecting the connection between the rectifier circuit and the 
series connection including the inductor is switched on within a switch 
interval of the current taken from the supply mains corresponds exactly to 
the load current corresponding to the mains voltage and necessary for 
obtaining its sinusoidal variation for the switch interval. 
Furthermore, it is advantageous if the switch arranged parallel to the 
series connection is controlled by a flip-flop circuit whose set input is 
connected to a pulse width modulator circuit whose input, in turn, is 
connected to the control line of the switch and to a differential 
amplifier comparing desired value with actual value, and whose reset input 
is connected to the pulse generator. As a result, as soon as the 
connection between the rectifier circuit and the series connection 
including the inductor is interrupted and, therefore, the discharging of 
the inductor serving as intermediate store begins and the difference 
between the actual value and the desired value of the direct voltage 
applied to the load falls below a minimum value, which is equivalent to a 
sufficient energy delivery to the load circuit, the further delivery of 
energy is interrupted until the switch interval determined by the pulse 
generator has elapsed.

DESCRIPTION OF PREFERRED EMBODIMENTS 
A preferred embodiment of the circuit arrangement according to the 
invention is composed of a rectifier circuit 2, for example, realized by 
four diodes in a bridge circuit, a storage inductor 6, two controlled 
switches 3 and 4 connected in series or parallel to the storage inductor, 
a diode 7, a storage capacitor 8 and a regulator circuit. A high-frequency 
energy filter in the form of an LC network prevents reactive effects on 
the supply mains which could be caused by the switching operations of the 
switches 3 and 4. 
The preferred embodiment of the invention illustrated in FIG. 2 includes a 
mains circuit, composed of an energy filter circuit 1, a rectifier circuit 
2 and the series connection composed of a controlled switch 3 of the 
storage inductor 6 and a current sensor 10. Another circuit, the storage 
circuit, is formed by the series connection composed of the other 
controlled switch 4, the storage inductor 6 and the current sensor 10. 
Finally, the load circuit is formed by the series connection of the 
storage inductor 6, with the current sensor 10, a diode 7, the load 9, and 
a parallel capacitor 8, however, the latter is necessary for the circuit 
only in the event that the load 9 does not itself exhibit an integrating 
behavior. A regulator circuit 5 controls the opening and closing times for 
the load voltage and the current flowing thorugh the current sensor 10. 
The principle manner of operation of the circuit is illustrated by FIG. 1. 
FIG. 1a shows the variation of the mains voltage and the sinusoidal 
variation of the mains current enforced by the action of the regulator 
circuit 5. Underneath FIG. 1a, FIG. 1b shows the constant load voltage and 
the constant load current as direct current values. 
The diagram of FIG. 1c shows the instantaneous power picked up the supply 
mains. The diagram shows, as a product of sinusoidal mains current and 
sinusoidal mains voltage, the variation of the power which is also 
sinusoidal and which oscillates with twice the frequency of the current 
taken by the circuit from the supply mains. 
The average power also represents that power which is delivered to the load 
9 multiplied by the efficiency of the circuit. 
The main object of the circuit arrangement according to the invention is to 
temporarily store as current in an inductor that power/time area (energy) 
illustrated with shading in FIG. 1c, which is determined by that power 
which is picked up from the mains in accordance with the sinusoidal mains 
current, but exceeds the constant power delivered to the load, and to 
deliver this current to the load 9 as soon as the power to be delivered to 
the load 9 falls below the power picked up from the mains. 
This manner of operation is achieved by periodically opening and closing 
the switches 3 and 4, so that the currents averaged over the switch period 
.tau. in the mains circuit as well as in the load circuit satisfy the 
required boundary conditions, such as, sinusoidal mains current and 
constant load current. The forms of current which occur as a result are 
explained with the aid of FIGS. 3a-3d. The switch interval t is divided 
into three portions. t.sub.1 is that time period in which the mains 
circuit is closed, while t.sub.2 is that time period in which the load 
circuit is closed, and, in the remaining portion t.sub.3 of the switch 
interval t, energy is neither picked up from the mains nor is energy 
delivered to the load. The switches 3 and 4 are designated by the 
reference symbols S.sub.1 and S.sub.2. FIG. 3b shows the flow of the 
current through the inductor over time. 
At the beginning of the switch interval t, switch 3 is closed while switch 
4 is opened. Accordingly, the mains circuit is closed and, therefore, the 
current flowing through the inductor 6 increases in accordance with the 
law of induction, 
##EQU1## 
When it is assumed that the switch interval t is short as compared to the 
mains period duration, the mains voltage may be considered constant during 
a switch interval. Thus, 
##EQU2## 
for the coil current at the end of the interval t.sub.1. 
In order to observe the requirement for a sinusoidal mains current, the 
switched-on duration t.sub.1 must be determined by the regulator circuit 5 
in such a way that the average value of the current taken from the supply 
mains during a switch interval corresponds exactly to the current 
corresponding to that for obtaining a sinusoidal variation of the mains 
voltage for the switch interval. 
##EQU3## 
FIG. 3c shows the variation of the mains current i.sub.N over time during a 
switch interval t, as well as the corresponding average taken over the 
switch interval t, which is apparent from the equal size of the two shaded 
areas. 
After the end of phase t.sub.1 of the switch interval, switch 3 is opened 
and, due to the tendency of the coil current to continue to flow in the 
same direction as before, the diode 7 becomes conductive and the load 
circuit is thereby closed. The coil current flows into the load, on the 
one hand, and into the storage capacitor 8, on the other hand. 
When the energy stored in the capacitor 8 is large in comparison to the 
quantity of energy transported in a switch period, the voltage at the 
capacitor 8 and, therefore, the voltage at the load can be considered 
constant during a switch interval. 
The storage current i.sub.S decreases in accordance with the law of 
induction until the switch 4 is closed and the current is thereby diverted 
from the load circuit into the storage circuit. The interval t.sub.2 is 
selected such that the average of the load voltage, of the load current, 
or of the load power is constant. FIG. 3b shows the variation over time of 
the current flowing through the diode 7 and the average of the current 
derived therefrom, averaged over a switch interval. 
During the breaks in the diode current, the load is supplied by the energy 
stored in the capacitor 8. From this, a dimensional specification can be 
derived for the size of the capacitor 8, depending upon the permitted 
waviness of the current. During the third partial interval t.sub.3, energy 
is neither taken from the mains nor is energy delivered to the load 
circuit via the diode 7, rather, the magnetic energy is stored in the coil 
6 as circuliar current. 
FIG. 4 shows the internal circuit of the regulator circuit designated by 
reference numeral 5 in FIG. 2. For regulating the phase or time period 
t.sub.1, the current sensor 10 generates a signal proportion to the 
instantaneous pulse current. This signal is combined through an analog 
gate circuit ATS with the control signal of switch 3 and is applied to a 
differential amplifier DV1 over an averaging unit MWB. This signal is 
proportional to the actual value of the mains current. The other input of 
this differential amplifier DV1 receives a desired current value signal 
which is derived from the mains voltage or is generated synchronously with 
the mains voltage and which is picked up by the potentiometer PT. The 
output of the differential amplifier DV1 controls a pulse width modulator 
circuit PWM1 whose output, in turn, represents the control signal for 
switch 3. The pulse width modulator control circuit PWM1 is triggered by a 
pulse generator TG. The regulator circuit for determining the time period 
t.sub.2 during which the load circuit is closed and for determining the 
load over the current path, i.e., diode 7, capacitor 8, load 9, current 
sensor 10 formed by a resistor and closed by inductor 6, includes a 
differential amplifier DV2 at whose one input there is applied a signal 
proportional to the instantaneous load voltage and to whose other second 
input there is applied a signal proportional to the desired value of the 
load voltage. The output of this differential amplifier DV2 controls a 
pulse width modulator circuit PWM2 which is triggered by the output signal 
of the pulse width modulator circuit PWM1. The output of the pulse width 
modulator circuit PWM2 is not used directly as switch control signal, but 
it sets a flip-flop circuit FF. This flip-flop circuit FF determines the 
control signal of switch 4. The flip-flop circuit FF is set by the pulse 
generator TG at the beginning of the next switch period. The pulse 
generator TG generates pulses of constant frequency and controls the two 
pulse width modulator circuits PWM1, PWM2 and the flip-flop circuit FF 
required for controlling switch S.sub.4. 
The circuit ensures the pre-processing of the mains current by the analog 
gate circuit ATS and the series-connected averaging unit MWB. For forming 
the actual value of the mains current, only the coil current during the 
time period t.sub.1 may be used. This is ensured by the analog gate 
circuit ATS. However, without changing the regulating principle, the 
analog gate circuit ATS can also be replaced by a second current sensor 
circuit in the load circuit, which is then directly connected in series 
with the averaging unit. 
It is unnecessary to pre-process the direct voltage which is regulated so 
as to be constant and this voltage can be applied directly to the 
differential amplifier DV1, DV2, where a comparison of desired value with 
actual value is carried out. Differential amplifiers are to be understood 
as those amplifier circuits with series-connected regulator amplifiers 
which determine a certain time behavior. Accordingly, this concerns itself 
not with simple operation amplifiers, but amplifiers with additional 
low-pass filter characteristics. The averaging unit can be realized by a 
commercially available averaging circuit. Another conceivable embodiment 
for this is a controlled integrator circuit in which the capacitor 
determining the integrating behavior can be bridged in a controlled 
manner. As a result, by a specified storing of current in a coil 6 or by a 
specified withdrawal of this energy from this coil 6, a sinusoidal 
variation of the mains current is obtained, as also is obtained a constant 
power delivered to the load. 
FIG. 5 shows an embodiment of the circuit arrangement according to the 
invention wherein the rectifier circuit is replaced by four switches 51, 
52, 53, 54 which are controlled in a sense of a rectification. These four 
switches also assume the function of the switch 3 according to FIG. 2 
which effects the separation from the AC mains. These four switches are 
controlled by the regulator circuit 55 which also controls switch 4 
connected in parallel to the series connection composed of inductor 6 and 
current sensor 10. The separation of the capacitor 8 and the load 9 from 
the AC mains is effected by the switch 50 which is also controlled by the 
regulator circuit 55.