Method and control system for transforming an AC voltage into a consumer supply voltage with adjustable rms value

0001The present invention relates first of all according to the preamble of claim 1, a method for converting a particular single-phase or multi-phase, of their phase angle particular sinusoidal AC supply voltage in a respect to their effective value adjustable operating voltage for an electric motor, especially for a single-phase induction motor for the purpose of speed control. Such a method results from the document<patcit id="pcit0001" dnum="US5498946A"><text>US-A-5498946</text></patcit>,

0002The invention also relates to a control system further according to the preamble of claim 8 having a lying to the respective consumers in series adjusting means. To such a control system is to the document<patcit id="pcit0002" dnum="EP1343357A2"><text>EP 1343357 A2</text></patcit> spoil.

0003The invention specifically relates to providing an operating voltage for inductive or capacitive loads, in particular for single-phase asynchronous motors, such. As capacitor motors or shaded pole motors, could in principle be applied for resistive loads above.

0004It is known to a AC supply voltage, in particular a sinusoidal mains alternating voltage, transforming adjustable operating voltage via an adjusting means in a with respect to its effective value.

0005<patcit id="pcit0003" dnum="JP58151896A"><text>JP, 58-151896, A</text></patcit> discloses a method and an apparatus wherein the linear drive by means of a transistor and the phase control are combined by means of thyristors for control of an AC electric motor.

0006The above-mentioned document <patcit id="pcit0004" dnum="US5498946A"><text>US-A-5,498,946</text></patcit> or the corresponding publication <patcit id="pcit0005" dnum="DE69403730T2"><text>DE 694 03 730 T2</text></patcit> describes a device - and, implicitly, a method - for controlling the power and / or speed variation of a load, such as an asynchronous, synchronous, universal motor, a transformer, an inductance, a capacitor or a resistor, the one on a one phase single- or multi-phase alternating-current supply circuit installed switch Zweirichtungsart with MOS, IGBT or bipolar transistor comprises, wherein this switch means for controlling the cyclical ratio α are / T associated with α to the duration of the opening or closing of the circuit by the switch, and T the period that phase, on which it is installed last, correspond. In this case, the switch circuit timing means are associated, which are suitable to prolong the switching time in the closure so that it lies within a range between 10 microseconds and 1 millisecond, whilst the means for controlling the cyclical ratio α / T also form means suitable are to control the opening of the AC power supply circuit through the switch when it is located in the coercive field of the magnetic circuit of the load, ie during a maximum time after the reversal of the current direction corresponding to a quarter of a half period T as long as a nominal-current tripping threshold, a third of the maximum rated current value corresponds to, is below.

0007The document <patcit id="pcit0006" dnum="EP1343357A2"><text>EP 1343357 A2</text></patcit> describes an electronic dimmer for controlling the power supply of a load, wherein an application is not specifically called for electric motors, but it is primarily concerned with control of luminaires. This known dimmer operates with a digital evaluation and control unit which drives a ramp generator. The dimmer includes an IGBT (insulated gate bipolar transistor) with several operating states. In a first operating state it is switched off and allows no current flow. In a second operating state it is switched on, and consequently allows a current which is limited by a connected circuitry. In a third, linear operation state, a current is allowed, which is limited to a value proportional to the gate voltage. The IGBT is connected to a rectifier bridge. The ramp generator produces a ramp voltage signal which is fed via an output to the gate of the IGBT in order to operate the IGBT in a linear region.

0008The similar publications <patcit id="pcit0007" dnum="US5629607A"><text>US-A-5,629,607</text></patcit> and <patcit id="pcit0008" dnum="US4633161A"><text>US-A-4,633,161</text></patcit> affect light dimmers and no supply for an electric motor.

0009Furthermore, so-called linear controllers are known wherein the location device to the consumer in series is configured as a variable resistor. Thereby, the operating voltage can be set in further sinusoidal shape with respect to their amplitude level, so that also changes the effective value of the surface integral. The operating voltage decreases with increase of the variable resistor. Is the resistance infinite, is the consumer at no voltage; the resistance will be reduced to 0 Ω, is the consumer the original AC supply voltage to, advantage of such a linear control is especially the always sinusoidal variation of the operating voltage, so that in case of the supply of an electric motor, smooth running with an ideal noise behavior is achieved, is a disadvantage, however, high power dissipation in the actuator, notably when the voltages on Steep and the consumers are about the same size. In addition, the adjuster resistance has to be designed for the maximum power dissipation, which results in a large construction and high cost.

0010Furthermore, a phase control is known, wherein the location means substantially consists of a triac which is connected via a control unit be controlled such that at the beginning of each half sine wave in its width (phase angle) of the variable part of each sinusoidal half-wave is cut away so that the remaining residues of the half-waves lead to a variable RMS as surface integral. The effective value decreases with increasing lead angle. The advantage of a phase control with respect to a linear control is a lower power dissipation on regulator and a high fundamental frequency content up to a certain phase-angle of about 72 °. Further, the circuit complexity is relatively low and the size small. but very disadvantageous is not continuous, ie no longer sinusoidal variation of the operating voltage and the resulting current at the consumer. The non-sinusoidal loading can cause disturbances in the supply network. At a certain phase angle of z. B.> 72 °, the proportion of the fundamental content, whereby the share of harmonics increases decreases. A disadvantage arises particularly for electric motors, the thus generated noise out, which is perceived as very unpleasant "hum". This is very annoying especially in fan drives.

0011As technically really best solution frequency are often used. With a rectifier, a so-called DC link and a pulse inverter, a nearly sinusoidal supply voltage with a certain frequency and amplitude is generated. When used for the speed control of single-phase induction motors results in an ideal efficiency. However, the circuit scale is very large, so that a frequency converter for many applications are simply too expensive.

0012The same applies to so-called AC-chopper, which by pulse width modulation of the AC supply voltage (line voltage) with frequencies in the kHz range, only the amplitude of the consumer operating voltage is specified. The circuit complexity is comparable to that of a frequency converter. elaborate measures are required for the reduction of noise emissions due to the pulsed method, whereby this solution for speed control of single-phase asynchronous motors are also proving to be too expensive.

0013The present invention is based on the object of specifying a method of the kind and an appropriate control system to create, thereby minimizing the power loss with optimized noise behavior by minimizing the harmonic content of the operating voltage can be achieved, with a small and inexpensive outlay ,

0014This is achieved by a method according to claim 1, and by a control system according to claim 6 according to the invention. Advantageous embodiments are contained in the dependent claims. The AC supply voltage is variable in dependence on the phase angle in a range of 0 set to 1 factor so that the operating voltage predeterminable over the course of the phase angle with respect to their respective instantaneous values ​​using at least one predetermined function in each case by one over the phase angle away with by the function desired History of instantaneous values ​​from 0% to 100% of the corresponding instantaneous values ​​of the AC voltage can be generated. For this, the AC supply voltage controlled by a with respect to its conductivity variable actuator is converted in the operating voltage, wherein the actuator setpoint instantaneous values ​​are predefined for the operating voltage, wherein the desired instantaneous values ​​defined by multiplication of the respective instantaneous values ​​of the AC supply voltage with corresponding, by the function, for example, stored in a table of values ​​drive level values ​​are determined.

0015To the respective consumer means of transformer in series adjusting means consists of a controlled by the phase angle away with respect to its conductivity over a control range from 0% to 100% changeable to different values ​​and intermediate values ​​actuator, and this actuator is based on a control unit in dependence on the phase angle of the AC supply voltage at least one stored in a memory function with modulation depth values ​​are controlled such that the operating voltage on the phase angle of time can be generated with an arbitrarily predetermined or predeterminable by the function curve of instantaneous values ​​from 0% to 100% of the corresponding instantaneous values ​​of the AC supply voltage. It defines the respectively, each designed for a specific effective value of operating voltage and stored in the memory function control factor values ​​as factors in the range of 0 to 1 as a function of the phase angle of the AC supply voltage, the instantaneous values ​​of the AC supply voltage via a multiplier by means of the control factor values ​​can be changed. The / each function can be stored for example in the form of a stored value table. Alternatively, the drive level values ​​can be calculated depending on the phase angle by a stored algorithm each date ( "online").

0016By the invention it is possible to generate the operating voltage with technically simple and cost-effective means "synthetic" with a practically arbitrary phase angle profile. This phase characteristic of the operating voltage can be set, having essentially only the advantages of linear and phase control, but largely avoiding their disadvantages or at least minimize. So can be generated from one of several different functions for each particular rms operating voltage has its own, different phase response, so that over the entire operating range of the operating voltage across minimization of Steller power dissipation and a minimization of harmonic content of the operating voltage can be achieved. For this purpose, the memory means for storing a corresponding number of functions (eg. B. value tables, algorithms), which are each designed for a certain effective value with optimized phase response. From the stored functions (speed setting signal in the case of a motor) can then by setting a control signal each having a specific function can be selected, which is then used for controlling the actuator,

0017The invention can also be implemented relatively economically by the actuator having to be switched in series with the load power semiconductor arrangement which is preferably made of two oppositely series-connected power semiconductors. The power semiconductor device is adjustable with respect to their conductivity.

0018In the following the invention will be explained in more detail based on some embodiments. Show it:<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>a simplified schematic block diagram of a control system of the invention in a basic version,</dd><dt>Fig. 2 - 4</dt><dd>Diagrams for explaining the principle of the invention based on three possible examples of the phase to be generated during the operating voltage,</dd><dt>Fig. 5</dt><dd>an opposite <figref idrefs="f0001">Fig. 1</figref> detailed circuit diagram in another embodiment of the control system according to the invention,</dd><dt>Fig. 6</dt><dd>a more detailed diagram of an adjusting means in a preferred embodiment,</dd><dt>Fig. 7</dt><dd>a voltage diagram with an exemplary phase profile of the generated operating voltage relative to the AC supply voltage (line voltage)</dd><dt>Fig. 8</dt><dd>another circuit diagram of an inventive system similar <figref idrefs="f0005">Fig. 5</figref> in one embodiment for varying the effective value, in particular to speed setting of an asynchronous motor,</dd><dt>Fig. 9u.10</dt><dd>respectively in today faced partial figures a) and b) possible courses of drive level values ​​on the phase angle and resulting operating voltages for further explaining the principle of the invention,</dd><dt>Fig. 11 u.12</dt><dd>further diagrams similar <figref idrefs="f0007 f0008">FIGS. 9 and 10</figref>That does not however correspond to the inventive principle</dd><dt>Fig. 13</dt><dd>Diagrams for explaining a particular operation of the advantageous embodiment of the system of <figref idrefs="f0006">Fig. 8</figref> and </dd><dt>Figure 14</dt><dd>a further embodiment of the control system of the invention in an illustration similar <figref idrefs="f0005">Fig. 5</figref> and <figref idrefs="f0006">8th</figref>Wherein the operating voltage is generated indirectly via a setting and regulation of the consumer current.</dd></dl>

0019As from first <figref idrefs="f0001">Fig. 1</figref> yields, is a single-phase, sinusoidal AC supply voltage U_N, Usually a conventional supply system voltage of a simplified as a voltage source 1 AC voltage system shown, through a site means 2 in a respect to their effective value adjustable operating voltage U_M be formed for an electrical load. 4 The adjusting means 2 is to the consumer 4 upstream in series. The AC supply voltage U_N runs on its phase angle φ_N away especially sinusoidal, see for example <figref idrefs="f0006">Fig. 7</figref> and <figref idrefs="f0010">13</figref>Where the phase curve normalized by the ratio U_N : U_nmax is shown. As a consumer, 4 in particular to an electric motor M (<figref idrefs="f0001">Fig. 1</figref>) Or concrete, a single-phase induction motor (ASM<figref idrefs="f0005">Fig. 5</figref>. <figref idrefs="f0006">8th</figref> and <figref idrefs="f0011">14</figref>) Are driven.

0020According to the invention to the point means 2 of a special actuator 6, which is simplified in the drawings with the symbol of a variable resistor located. However, it is not a simple resistor, rather the actuator 6 is - see also the detailed example in<figref idrefs="f0005">Fig. 6</figref> - So quickly adjustable in terms of its conductivity or its internal resistance that φ on the phase angle_N of time with respect to its conductivity controlled by a control range from 0% to 100% to different values ​​and intermediate values ​​can be changed. In this case, the actuator 6 by a control unit 8 in dependence on the phase angle φ is inventively_N with so-called modulation depth values ​​AT least one based in a memory 10 stored function AM = f (φ_N) Is controlled such that the operating voltage U_M φ on the phase angle_N away with an arbitrarily predetermined or predeterminable by the deposited functional profile of instantaneous values ​​U_M'Is from 0% to 100% of the corresponding instantaneous values ​​U_N'The AC supply voltage U_N can be generated. In this case, the respective function AM = f (φ_N), For example in the form of a value table 12 (12a, b, c) be stored in memory 10 (see FIG. <figref idrefs="f0005">Fig. 5</figref>. <figref idrefs="f0006">8th</figref> and <figref idrefs="f0011">14</figref>).

0021It is further shown <figref idrefs="f0001">Fig. 1</figref> yields, calculated a multiplier 14 from the respective drive level values ​​AM and the current actual values ​​(instantaneous values) U_N'The AC supply voltage U_N the default (set point) U_M'Of the operating voltage which is passed to the actuator. 6 The actuator 6 controls its internal resistance accordingly so that the consumer 4 supplied operating voltage U_M the default U_M'Corresponds as closely as possible. The voltage across the actuator 6 is as an actuator voltage U_S drawn; it is essentially the equation UM = U_N - Us.

0022It is essential that φ over the phase history_N of time, ie for example during a period T₀, Occurs a variation of the conductivity controller, ie a "dynamic conductance change" (as opposed to a static setting of a series resistor at a linear control).

0023The principle of the invention should now be based on the <figref idrefs="f0002 f0003 f0004">Figures 2 to 4</figref> are explained, in each case only a half period (half-wave) in the range φ = 0 to 180 ° is shown, because preferably the second half period (half-wave) identically (symmetrically) is controlled. In principle, it would also be possible to specify unequal or asymmetric profiles for the positive and negative half-waves, although this would generally decrease the efficiency of an induction motor ASM.

0024In <figref idrefs="f0002">Fig. 2A</figref> is an example of a possible course of the modulation depth value AM depending on the phase angle φ_N illustrated. In a first angle range 0 ° to φ₁ is the drive level deposited 0%, which means that the actuator 6 blocks, which according <figref idrefs="f0002">FIG. 2b</figref> as normalized ratio U_M': U_nmax illustrated operating voltage is 0 (on consumer 4 is no voltage). In a second angular range of φ₁ to φ₂ is the modulation depth AM continuously from 0% enlarged with a really arbitrary waveform to 100%, whereby the actuator 6 passes from locking in an increasingly conducting state. As exemplified in<figref idrefs="f0002">FIGS. 2a and b</figref> is located, is at a modulation depth AM = 50% of the instantaneous value of the operating voltage U_Malso '50% of the corresponding instantaneous value U_N'The AC supply voltage U_N, And AM = 75% is U_M'Also 75% of U_N'. From the phase angle φ₂ is AM = 1 corresponding to 100%, so that the operating voltage U_M exactly the way the AC supply voltage U_N follows.

0025In the second example according to <figref idrefs="f0003">Fig. 3</figref> has the function of modulation depth AM a reverse course, being in the angular range 0 ° to φ₁ the modulation depth is 100% deposited. This means that the actuator initiates 6, whereby the operating voltage U_M the course of the AC supply voltage U_N follows. In subsequent angular range φ₁ to φ₂ the AM modulation depth is reduced continuously to the stored function to 0%, whereby the actuator 6 changes from the fully conductive state through intermediate values ​​in the fully blocking state. From the angle φ₂ is the modulation depth AM 0%, so that the operating voltage U_M 0 is.

0026The third example in <figref idrefs="f0004">Fig. 4</figref> shows that the degree of modulation AM is changeable also to any other function. In a first angle range 0 ° to φ₁ as well as in an end region between φ₃ and 180 ° is the control factor A_M = 100% deposit, which means that the actuator 6 passes completely, so that in these angular ranges at the beginning and end of a half-wave, the operating voltage U_M the course of the AC supply voltage U_N follows. In a central angle range of φ₁ to φ₂ is in <figref idrefs="f0004">FIG. 4a</figref> deposited recognizable function, through which the drive level continuously to example 28.6% φ_N = 90 ° and then decreases again continuously to φ₃ is increased to 100%. The resulting variation of the operating voltage is given by<figref idrefs="f0004">Fig. 4b</figref>,

0027It should be noted that the diagrams in <figref idrefs="f0002 f0003 f0004">FIGS. 2-4</figref> are exemplary to understand. In addition to these exemplified possibilities for inputting the operating voltage any other courses below the envelope of the voltage are of course conceivable. This means that the operating voltage can be generated with basically any phase progression.

0028The operation of the invention is in the <figref idrefs="f0007 f0008">FIGS. 9 and 10</figref> explained.

0029In <figref idrefs="f0005">Fig. 5</figref> is in concrete form, another embodiment of the control system of the invention shown, in a mixed representation of a circuit diagram and partial block diagram. With a detection circuit 16, the AC supply voltage U_N monitored, and there are the phase angle φ_N and the instantaneous values ​​U_N'Recorded and 8 put the control unit. In this illustration, the control unit 8 includes the memory 10 as a "function block" and the multiplier 14. The modulation depth values ​​AM are exemplified in the form of a value table 12 with pre-calculated function values ​​in the function block (memory 10) stored. However, it can of course also as an algorithm, z. B. be stored in a microcomputer, the function values ​​depending on the instantaneous phase angle φ_N numerically at runtime (online) are calculated. Here, the function in closed form, z. B. as a polynomial or piecewise continuous behavior, consisting of straight or partial functions of a higher order, be described. Likewise, the definition in terms of an equation is possible to numerically by a common method, for. Example, Newton's method, is achieved at runtime (online). In the following embodiments, only the function definition in the form of stored tables of values ​​is used with pre-calculated function values ​​of illustration. Here, the stored modulation depth values ​​AM as a function of φ_N stored in the value table 12 in decimal or, for example, as suitable for a microcontroller binary values. In this example, each instantaneous value is U_N'The AC supply voltage to the associated drive level value AM multiplied in the multiplier 14th This results in a setpoint U_M'Of the operating voltage. In this embodiment, after<figref idrefs="f0005">Fig. 5</figref> a subtracter 18 is additionally connected downstream of the U by subtracting the respective instantaneous values_N'And U_M'According to the equation U_S'= U_N'- U_M'A specification or a setpoint U_S'For the Steller voltage U_S calculated. The actuator 6 then controls its internal resistance corresponding to the predetermined desired value U_S'So that U_S as precisely as possible U_S'Equivalent.

0030In <figref idrefs="f0005">Fig. 6</figref> exemplified a concrete embodiment of the actuator. 6 Accordingly, the actuator 6 is a power semiconductor arrangement 20, which preferably consists of two oppositely series-connected power semiconductors 22, 24 is made. These are, for example, MOSFETs. The actuator 6 also comprises an integrated voltage regulator 28 which will not be explained in more detail at this point. the MOSFET's are preferably controlled directly by the voltage regulation 28th Here, the respective control variable, z. B. the setpoint U_S'Should 1, are fed galvanically isolated via an optocoupler 26th

0031In <figref idrefs="f0006">Fig. 7</figref> is an example of a possible course for a generated operating voltage over a full period T₀ illustrates, in relation to the AC supply voltage. Here, the voltages are represented normalized. It can be seen that a relatively harmonic with respect to the half-shafts practically sinusoidal course of the operating voltage can be achieved.

0032As for the in <figref idrefs="f0006">Fig. 8</figref> relates illustrated embodiment of the inventive control system, so this is different for multiple relative to the RMS value of phase characteristics of the operating voltage U_M designed. This serves in particular to vary the speed of the motor ASM. For this purpose, the function block (memory 10) means for storing a plurality of, in each case for one with respect to the effective value different phase course of the operating voltage U_M designed functions or tables of values ​​(by way of example only three value tables 12a, b, c are shown). In each one of the plurality of functions or tables of values ​​via adjusting means 30 by setting a control signal S is selected. is then further controlling the actuator 6 based on the function or table of values ​​respectively selected. The adjustment range is divided into a plurality of steps, preferably carried out within a range of adjustment between two tables of values ​​that calculate the modulation depth AM by interpolation. Thus, the course of the modulation depth AM be changed with the control signal S advantageously continuously, resulting in a continuous change in speed in the application for an asynchronous motor ASM.

0033In connection with this embodiment is suitably the operating voltage U_M Generated by specifying and selecting the value tables 12a, b, c such that on the (speed) setting range of the operating voltage U_M away minimization of Steller power dissipation and a minimization of harmonic content of the operating voltage U_M be achieved. In this way, a "quasi-linear control" at the bottom of the effective value of the operating voltage or at a lower engine speed range and a "quasi-phase control" in the upper voltage / speed range reach, but with steady, continuous transitions. Thereby, the operating voltage U_M always generates a steady, at least approximately sinusoidal and therefore low harmonics causing history. General can thus be achieved a combination of the advantages of linear and phase control and virtually eliminates their disadvantages.

0034In <figref idrefs="f0007 f0008">Fig. 9</figref> and the partial figures a) to f) are exemplary multiple courses of the modulation depth AM illustrates how it can be stored depending on the control signal S in the value tables and used for interpolation. The<figref idrefs="f0007 f0008">Fig. 10</figref> shows the accordance of the dowry degrees AM in the respective associated sub-figures a) to f) <figref idrefs="f0007 f0008">Fig. 9</figref> resulting profiles of the operating voltage U_M or their nominal value U_M'That results from the multiplication of the respective instantaneous values ​​U_N'The AC supply voltage U_N result with the respective modulation depth AM. By the representations, the principle of voltage command is to be illustrated by various waveforms stored in individual steps. By interpolating between the curves of the modulation depth AM accordance<figref idrefs="f0007 f0008">Figs. 9a to f</figref> is possible within the adjustment range, a continuous change of the operating voltage in dependence on the control signal S. For large actuating signal S the full AC supply voltage is output, for example, over the entire period or half-period (<figref idrefs="f0007">Figs. 9a and 10a</figref>), Or it is a profile analogous to a phase control in accordance with <figref idrefs="f0007">Fig. 9b</figref> und10b used. With a small control signal S suitably carried the specification corresponding to a linear control (<figref idrefs="f0008">Fig. 9e</figref> und10e) until the operating voltage U_M has become the consumer 4 to zero (<figref idrefs="f0008">Fig. 9f and 10f</figref>). In between are inventively combined from phase control and linear control curves for example, according<figref idrefs="f0007">Fig. 9c, 10c, and Fig. 9d, 10d</figref> deposited. The course of the operating voltage varies continuously thereby from similar to a phase control to the similar to a linear control.

0035From the "quasi-phase control" in accordance <figref idrefs="f0007">Fig. 9b, 10b</figref> with a jump in the modulation depth AM the transition to the combined course carried out in accordance <figref idrefs="f0007">Fig. 9c, 10c</figref> continuously, for example by reducing the slope of the jump in the modulation depth AM by very large values ​​on the slope of the curve in accordance with <figref idrefs="f0007">Fig. 9c</figref>,

0036More, however, not included in the scope of the invention falling progressions are in <figref idrefs="f0009">FIGS. 11 and 12</figref> shown. These courses are particularly advantageous for use in fans with single-phase induction motor. Compared to<figref idrefs="f0007 f0008">FIGS. 9 and 10</figref> were according <figref idrefs="f0009">FIGS. 11 and 12</figref> only gradients deposited, which represent practically a combination of phase control and linear control. This stored functions of modulation depth AM through their low pitch to a compared to the pure phase control significantly better noise performance, which is a linear control comparable to, but at much lower losses than with linear control.

0037Below we have to a particular embodiment with reference to the example according to <figref idrefs="f0006">Fig. 8</figref> are explained. Accordingly, the control system and the control unit 8, an additional switching device 32, with which the actuator 6 in dependence on the phase of the course of the operating voltage U_M resulting load current I_M φ each have a specific phase angle₂ - φ₃ (S. To the chart in <figref idrefs="f0010">Fig. 13</figref>) Away deactivated, ie blocking entirely in a high-impedance state is switchable. This is a "hard shutdown" as opposed to a drive with a drive level AM = 0. For this purpose, generates the switching device 32 depending on the load current I_M a switching signal S_{on / off} for the actuator 6. In order to function this advantageous measure is made to the diagram in <figref idrefs="f0010">Fig. 13</figref> pointed. There is an example of a typical for capacitor motors load current I_M shown. φ the time₁ or φ₃When each of the modulation degree of 0% is transferred to larger values, is capitalized (switching on) of the actuator 6 to the control signal S_{on / off} = 1. Activation and switching means that the actuator 6 from the off state to the default of Steller voltage U_S = U_S'Switches. φ the time₂ or φ₄When the load current I_M has dropped down to 0, there is a shutdown of the regulator by S_{on / off} = 0 to zero after becoming the consumer current I_M To avoid a further increase which would occur due to the course of the internal voltage of the motor. This results in the actuator behaves as a static switch (triac or thyristor), whereby a curve can be generated similar to a phase control. The current I_M Here, either of the voltage U_N at the time of zero becoming advancing (capacitive behavior) as shown in <figref idrefs="f0010">Fig. 13</figref> shown or lagging (inductive behavior).

0038In a further advantageous embodiment, in addition to the previously described methods, wherein the operating voltage in dependence on the phase angle φ_N and the control signal (modulation depth AM) is defined in different progressions, in an analogous manner, the course of the load current I_M be specified directly, for example via a subtractor 34 with a downstream current controller 18, the output of the actuator voltage U_S'Should the envelope of the mains voltage U_N' limited. Such training is in<figref idrefs="f0011">Fig. 14</figref> shown. The modulation depth AM is similar to the embodiment of<figref idrefs="f0006">Fig. 8</figref> deposited in the form of value tables 12a to 12c depending on the actuating signal S as different functions. but this does not refer to the drive level directly on the voltage, but first to the current value I_M'. The multiplier 14 calculates this φ from the deposited modulation depth AM, the current phase angle_N and the stored maximum current I_M'max the preset for the target value of the motor current I_M', Which is fed for comparison with the actual value of the subtracter 34th According to a deviation between actual value and desired value of the current, the control signal for the actuator 6 by conventional control engineering method is determined. This function can, for example, assume an analog or digital executed PID controller. By interpolation between the stored waveforms of the modulation depth, a continuous setting of the load current in dependence on the actuating signal S is possible within the adjustment range, as was also analogously described already for the case of the voltage command. In the example shown, the control signal in the form of the voltage command U_S'_Should within the range of the instantaneous AC supply voltage U_N'Passed from the controller 8 to the actuator. 6