Patent Document

This application is a National Stage of International Application No. PCT/EP2012/073725 filed Nov. 27, 2012 which claims the benefit and priority of German Application No. DE102011056941.3 filed Dec. 22, 2011 which are all hereby incorporated by reference. 
     TECHNICAL FIELD 
     The invention relates to a controller for a converter, wherein the controller is designed to receive from a measuring device measurement signals on an output line of the converter, and to analyze the measurement signals in order to generate a switching signal that has a switching frequency, wherein the controller comprises a sampler for generating a sample signal by sampling received measurement signals. If the converter is a multiphase converter, the output line is typically a phase line, the output current of which contributes to a total load current that is obtained by summating the currents of a plurality of phase lines. The switching frequency is typically a fundamental frequency (preferably the lowest fundamental frequency) of the switching cycle of the switches of the converter. 
     In addition, the invention relates to a converter comprising a controller designed to receive measurement signals from a measuring device on an output line of the converter and to analyze the measurement signals in order to generate a switching signal that has a switching frequency, wherein the controller includes a sampler for generating a sample signal by sampling measurement signals, and wherein the sampler is designed to perform the sampling at a sampling frequency that is less than three times the switching frequency. 
     The invention also relates to a control method for operating a converter, wherein the control method comprises the following steps: generating measurement signals on the basis of an electrical status of an output line; generating a sample signal by sampling the received measurement signals at a sampling frequency; analyzing the sample signal; and generating a switching signal at a switching frequency. 
     BACKGROUND 
     DE 10 2009 027 307 A1 describes a multiphase DC/DC converter. Each phase has a dedicated current sensor that supplies current values to a converter control element. The current control element generates on the basis of a reference current and received current values, gate driver signals for switching the phases. In an alternative arrangement, only one current sensor is provided, which measures the total load current and hence generates a current information signal for the load current that is obtained from the summated load current of a multiplicity of phases. 
     SUMMARY 
     The object of the present invention is to provide a controller for a converter that can be produced more cheaply than known controllers. It is also an object of the invention to provide a converter and a control method that can be operated using a controller that can be produced cheaply. 
     This object is achieved by the independent claims. The subject matter of the subclaims contains advantageous developments of the inventive idea. 
     The invention develops the controller by designing the sample to perform the sampling at a sampling frequency that is less than three times the switching frequency. As a result, for the subsequent signal analysis, a typical period is composed of measurement values from a plurality of (contiguous or non-contiguous) periods. By virtue of the subsampling, the upper frequency limit and bandwidth of the signal to be analyzed after sampling are lower than in the known controller. The subsampling and smaller bandwidth result in lower speed requirements for analyzing the sampled signals, and the controller is cheaper to produce. The sampling frequency can be a mean sampling frequency. It can be defined as the inverse of a mean value of the time intervals between successive time-contiguous trigger signals for opening the gate of the sampler for the purpose of defining points in time for taking measurements of the measurement signal. 
     The sampler can be designed to perform the sampling, for a switching frequency, at a mean sampling frequency, where neither the quotient of the mean sampling frequency divided by the switching frequency is a whole number nor the quotient of the switching frequency divided by the mean sampling frequency is a whole number. Satisfying this condition means that a plurality of interpolation points are captured by sampling a plurality of periods of a periodic signal waveform, and the high frequency signal, having a time scale equal to the ratio of the switching frequency to the difference between switching frequency and sampling frequency, can thereby be mapped onto a low frequency signal. If the sampling frequency is higher than the switching frequency, the difference, and hence the time scale, is negative. This means that the mapping of the high frequency signal then appears as a mirror image in the time domain. The mirror image in the time domain can be reversed again by swapping over interpolation values during the analysis of the low frequency signal. 
     The switching-signal generator can be designed to generate the switching signal at a switching frequency that is greater than the sampling frequency at least by the factor n, where n equals 5/6, 21/20, 11/10, 6/5, 2, 4, 8, 16, 32, 64 or another power of two. The choice of the factor n determines the speed and accuracy at which the original signal can be reproduced. The factor also determines the required performance of the controller. It should be mentioned to aid understanding that a sampling frequency that is more than twice as high as the switching frequency is generally still far from satisfying the Nyquist criterion. This is because the load signal usually contains not only the fundamental frequency of the switching process but significantly higher frequency components, the information content of which is meant to be retained until the subsequent analysis. This information can be used, for instance, to detect in the signal to be analyzed, relative lengths of the edges and the dead time, and to analyze same. 
     The sampler can be designed to perform the sampling using successive trigger signals, wherein a density function for time intervals between successive time-contiguous trigger signals comprises one or more Dirac delta functions and/or a continuous density function. A noise spectrum of the controller can be improved by sampling using different time intervals between time-contiguous trigger signals (gate signals). 
     The controller can be designed to determine from the sample signal at least one first type of statistical values. By reducing the measurement data to a few informative, aggregate values, subsequent analysis steps and generating the switching signal can be implemented more clearly and cheaply. 
     The at least one first type of statistical values can include maximum values, minimum values, effective values, arithmetic mean values and/or median values. 
     The controller can comprise at least one first comparator in order to compare a first setpoint value with a first actual value, which can be determined from the sample signal, and to determine from the result of the comparison a first correcting variable. For example, the first setpoint value and the first actual value may be an output current, an output voltage or a spectral characteristic of one or more of these variables. 
     The controller can comprise at least one second comparator in order to compare a second setpoint value with a second actual value, which can be determined from the sample signal, and to determine from the result of the comparison a second correcting variable. The second setpoint value and the second actual value can again be, for instance, an output current, an output voltage or a spectral characteristic of these variables. 
     The sample signals can be analyzed with regard to an output current, an output voltage and/or a spectral characteristic of one or more of these variables on the output line. 
     The controller can be designed to control a minimum output current for a falling edge of an output current. The output current is typically the current on an output line of a phase. 
     The controller can be designed to control a peak current, an effective current, a mean current or another characteristic of the output current for a rising edge of an output current. Again in this case, the output current is typically the current on an output line of a phase. 
     The controller can be designed to receive measurement signals from at least two phase-specific output lines, to sample the received measurement signals, to generate the sample signals, and to generate the switching signals. The controller can thereby be used simultaneously for two or more phases. In addition, cross-phase coordination between the phases is possible within the controller, for example for coordinated execution of a start-up cycle, for coordinated shutdown in the event of a fault or for load or current distribution in normal operation. 
     The converter of the present invention is developed by comprising at least one controller in accordance with the invention. The above-mentioned advantage can thereby be used for the converter. 
     The converter can comprise a load-current distributor for distributing a load current to a plurality of phases. A maximum power rating for the switching paths of individual phases can hence be fully utilized (with the inclusion of a safety margin), thereby avoiding costly overdesign of the switching paths of individual phases. 
     The control method of the present invention for operating a converter is developed by the switching frequency being three times higher than the sampling frequency. The resulting advantages have been described in the introduction. 
    
    
     
       DRAWINGS 
       The invention is explained in greater detail below with reference to exemplary embodiments illustrated in the schematic drawings, in which: 
         FIG. 1  illustrates a block diagram of a circuit having an electrical power source, an embodiment of a converter and an electrical load; 
         FIG. 2  illustrates a timing diagram comprising an example of switching signals from the converter controller, an example of a waveform of the output current from the converter, and an example of a waveform of the current measurement signal after sampling; 
         FIG. 3  illustrates an example of an embodiment having a density function, shown schematically, for time intervals between successive time-contiguous trigger signals of the sampler; 
         FIG. 4  illustrates a block diagram of an embodiment of a load current distributor; 
         FIG. 5  illustrates a flow diagram of an embodiment of a control method for operating a converter. 
     
    
    
     The same reference signs are used for corresponding components in each of the figures. Explanations that refer to reference signs therefore apply to all the figures unless the context dictates otherwise. 
     DESCRIPTION 
       FIG. 1  illustrates a circuit arrangement  10  having a voltage source  12  as an electrical power source, a converter  14  and an electrical load  16 . The converter can be a single-phase or multiphase converter, can be galvanically isolated or not galvanically isolated, unidirectional or bidirectional. The electrical power source  12  can be a DC voltage source, an AC voltage source, a DC current source or an AC current source. The electrical load  16  can comprise reactive components in addition to resistive components. The converter  14  comprises for a first phase a first switch S I , a second switch S II , an inductance L and a converter controller  18 . Both switches S I , S II , are single-pole switches. The first switch S I  is typically a semiconductor switch, for example a MOSFET or an IGBT (insulated gate bipolar transistor). The second switch S II  is typically the same type of semiconductor or is a flyback diode. A first terminal  21  of the first switch S I  is connected to the voltage source  12 , and a second terminal  22  of the first switch S, is connected to the inductance L. It is indicated in the figure that the converter  14  can comprise a plurality of circuits SK I  . . . SK n  of identical design for one or more further phases between converter input  14   a  and converter output  14   b . These circuits then typically operate using switching cycles D, F, B in intermittent mode and D, F in non-intermittent mode (see  FIG. 2   a ), which cycles have a different time offset from one another. Unless stated otherwise, the following description explains the converter controller  18  for the first phase. The concepts described can be applied to further phases. 
     A switching-signal generator  24  (modulator) generates a first switching signals SS, for actuating the first switch S I . The first switching signals SS, are transmitted via a first control connection SV I  to the first switch S I . In the exemplary embodiment shown, the switching-signal generator  24  also generates second switching signals SS II  for actuating the second switch S II . The second switching signals SS II  are transmitted via a second control connection SV II  to the second switch S II . The converter  14  can alternately adopt the following three operating states D, F, B: a conducting state D, a flyback state F and a standby state B. 
     In the standby state B, the switching-signal generator  24  controls the two switches S I , S II , such that the flow of the output current I L  is stopped. In the conducting state D, the switching-signal generator  24  controls the switches S I , S II  such that an output current I L  can flow through the first switch S I  but is stopped for the second switch S II . In the flyback state F, the switching-signal generator  24  controls the switches S I , S II  such that an output current I L  can flow through the second switch S II  but is stopped for the first switch S I . During operation under partial load, the three operating states D, F, B alternate cyclically in the following sequence: conducting state D, flyback state F, standby state B. When the amount of power transferred between the electrical power source  12  and electrical load  16  is low, the conducting state D, i.e. the proportion of time of the conducting state D compared with the switching period, is small. As the amount of power transferred between converter input  14   a  and converter output  14   b  increases, the proportion of time of the conducting state D compared with the switching period increases. A person skilled in the art knows numerous possible embodiments for converter switching patterns that can also be used here. These switching patterns are not explained below because these details are not essential to the invention. 
     The converter controller  18  is part of an open-loop control circuit, which comprises at least one first control loop comprising the following components: a controlled system RS, a first comparator  28   a  for comparing a first reference value FG a  with a first controlled variable RG a , a first closed-loop controller  30   a  and a final control element  24 , S I , S II . In the exemplary embodiment illustrated in the figure, the controlled system RS is formed by the power source, the input filter (not illustrated), the switches, inductance L, output filter (not illustrated) and the load. The final control element  24 , S I , S II  is formed jointly by the switching-signal generator  24  and the two switches S I , S II . The proportion of time of the flyback state F compared with the total period of the switching cycle D, F, B acts as the first correcting variable SG a . The minimum min(I L ) of the output current I L  output by the converter  14  to the electrical load  16  acts as the first controlled variable RG a . The first controlled variable RG a  is obtained by means of a phase-specific current sensor  34  for detecting an intensity of an output current I L1  on an output line  35  of a phase of the converter  14 , and by means of a sampler  36  and a subsequent current-signal analyzer  37 . The sampler  36  and the signal analyzer  37  are components of the converter controller  18 . The first comparator  28   a  determines a first error signal e a  by means of a first comparison of the first reference value FG a  with the first controlled variable RG a . The first closed-loop controller  30   a  (for example a PID controller) determines the first correcting variable SG a  from the temporal waveform of the first error signal e a . 
     The exemplary embodiment illustrates a second control loop, which comprises some of the same components  24 ,  34 ,  36 ,  37 , L, S I , S II  as the first control loop. The second control loop includes the following components: the controlled system RS, a second comparator  28   b  for a comparison between a second reference value FG b  and a second controlled variable RG b , a second closed-loop controller  30   6  and the final control element  24 , S I , S II . The inductance L again forms the controlled system RS. As in the first control loop, the final control element  24 , S I , S II  is formed jointly by the switching-signal generator  24  and the two switches S I , S II . In the second control loop, the proportion of time of the conducting state D compared with the total period of the switching cycle D, F, B acts as the second correcting variable SG b . A second characteristic value of the power transfer by the converter  14  acts as a second controlled variable RG b . This can be, for example, a maximum, a mean or an effective value of the output current I L  output by the converter  14  to the electrical load  16 . In the exemplary embodiment, the second controlled variable RG b  is obtained using the same current sensor  34 , the same sampler  36  and the same signal analyzer  37  as the first controlled variable RG a . A selector switch  33  can be used to select the second controlled variable RG b  from a plurality of alternatives (for example types of mean values). The second comparator  28   b  determines a second error signal e b  by means of a second comparison of the second reference value FG b  with the second controlled variable RG b . The second closed-loop controller  30   b  (for example also a PID controller) determines the second correcting variable SG b  from a temporal waveform of the second error signal e b . Only the peak current is controlled directly by the rising edge. All the other calculated values (such as effective values, mean values) are based on the complete signal, but can also be set with the rising edge. 
       FIG. 2   a  illustrates an example of a temporal waveform of the first switching signal SS I  for switching on es I  and switching off as II  the first switch S I  of the converter  14  during the conducting state D, during the flyback state F and during the standby state B. The boundaries of the time periods of the operating states D, F, B are illustrated in  FIGS. 2   a  to  2   d  by dashed lines.  FIG. 2   b  illustrates an example of an associated temporal waveform of the second switching signal SS II  for switching on es II  and switching off as II  the second switch S II  of the converter  14 .  FIG. 2   c  illustrates an example of an associated temporal waveform of the output current I L , of a phase of the converter  14 . In the conducting state D, the intensity of the current I L  through the output line  35  rises. Hence during the conducting state D, a rising edge  38  develops in the temporal waveform of the output current I L . In the flyback state F, the current I L  through the output line  35  falls. Hence during the conducting state, a falling edge  39  develops in the temporal waveform of the output current I L .  FIG. 2   d  illustrates an example of an associated temporal waveform of a sample signal S SAMPLE  after sampling  120  by means of the sampler  36 . The dash-dotted lines in  FIGS. 2   c  and  2   d  illustrate an example of a pattern for sampling the output current I L  by the sampler  36 . In the example illustrated in  FIGS. 2   c  and  2   d , sampling  120  of the output current I L  is performed almost once every switching period, wherein the sampling  120  in the immediately following switching period in each case (relative to the start thereof) is performed slightly later than in the immediately preceding switching period (relative to the start thereof). The sampling cycle is asynchronous with the switching periods of the switching signals SS I , SS II . As a result of the slippage between the sampling cycle and the switching signals SS I , SS II , the sampling  120  maps the temporal waveform of the intensity of the output current I L1  of a phase into a sample signal S SAMPLE  having a similar waveform but longer time scale, i.e. lower frequency f SAMPLE . In an alternative (not illustrated explicitly in the fig.), the second correcting variable SG b  can be a preset reference value (instead of being provided by the second closed-loop controller  30   b ). 
     In a further preferred alternative, the second correcting variable SG b  can be provided by a voltage regulator  40  or by a load-current distributor  42 . 
       FIG. 3  illustrates an example of an embodiment having a density function H(T dist ) for time intervals between successive time-contiguous trigger signals of the sampler  36 . Here, a mean sampling frequency f SAMPLE  is defined as the inverse of a mean value of the time intervals T dist  of successive time-contiguous trigger signals TS for opening the gate of the sampler  36  for the purpose of defining points in time for taking measurement values of the measurement signal SM. 
       FIG. 4  illustrates a schematic block diagram of an embodiment of a load-current distributor circuit  43 , which generates such a second correcting variable SG b  for each phase. Here, the output voltage U from the converter  14  is compared in a comparator  28   b1  with a setpoint voltage U SOLL , and the second correcting variable SG b1  for the first phase is generated by means of a voltage regulator  40   1 . 
     For the second phase, the output current I L1  of the first phase is first compared with the output current I L2  of the second phase. The current difference I L2 −I L1  is in turn compared with a current difference ΔI L2  defined as the reference value. A comparator  28   b2  determines therefrom an error signal e b2 =I L2 −I L1 −ΔI L2 , on the basis of which a second current regulator  41   2  determines a first contribution to a second correcting variable SG b2  of the second phase. The second correcting variable SG b2  is formed by combining  44   2  (preferably summating) the first contribution with the second correcting variable SG b1  of the first phase. 
     Correspondingly for further phases i (where i is between 3 and nεN), the output current I L1  of the first phase is first compared with the output current I Li  of the further phase i, and a further current regulator  41   i  of the further phase i is used to generate from the current difference I Li -I L1  (equals the error signal e bi ) a first contribution to a second correcting variable SG bi  of the further phase i. The second correcting variable SG bi  of the further phase i is also formed by combining  44   i  (preferably by summating) the first contribution with the second correcting variable SG b1  of the first phase. 
       FIG. 5  illustrates a schematic flow diagram of an embodiment of a control method  100  for operating a converter  14 . The control method  100  comprises the following steps  110 ,  120 ,  130 ,  140 : generating  110  measurement signals SM on the basis of an electrical status I L1  of an output line  35  by means of a sensor  34 ; generating  120  a sample signal S SAMPLE  by sampling the received measurement signals SM by means of a sampler  36  at a sampling frequency f SAMPLE ; analyzing  130  the sample signal S SAMPLE  and generating  140  a switching signal SS I  at a switching frequency f SW , wherein the switching frequency f SW  is higher than the sampling frequency f SAMPLE . The controller  18  for a converter  14  is designed to analyze the received measurement signals SM and to generate for the rising edge  38 , measurement signals SM that are independent of measurement signals SM generated for the falling edge  39 . 
     The concept in accordance with the invention can be applied to different types of converters, in particular also to DC-DC converters, inverters and/or frequency converters. The switching principles described can also be applied with the reverse polarity. Analog and/or digital electrical signals that are represented in the exemplary embodiments in the form of voltages can be represented alternatively or additionally as (impressed) currents. Amplifiers or converters can be used to modify the magnitude of voltages or currents mentioned in the description in the path from their respective sources to their respective sinks. Analog or digital signals that are represented in the form of voltages or currents can be linearly or non-linearly encoded in accordance with a known method or a method that is not yet known today. Examples of applicable coding methods are pulse width modulation and pulse code modulation. The analog and/or digital signals can be transmitted electrically, optically or by radio. The analog and/or digital signals can be transmitted in a space-division multiplex (i.e. using different lines), in a time-division multiplex or in a code-division multiplex. The analog and digital signals can be transmitted via one or more bus systems. 
     LIST OF REFERENCE SIGNS 
     
         
           10  circuit arrangement 
           12  electrical power source 
           14  converter 
           14   a  converter input 
           14   b  converter output 
           16  electrical load 
           18  converter controller 
           21  first terminal of the first switch S I    
           22  second terminal of the first switch S I    
           24  switching-signal generator 
           28  comparator 
           30  closed-loop controller 
           33  selector switch 
           34  measuring device; current sensor 
           35  output line 
           36  sampler 
           37  signal analyzer 
           38  rising edge 
           39  falling edge 
           40  voltage regulator 
           41  current regulator 
           42  load-current distributor 
           43  load-current distributor circuit 
           44  combiner 
           100  control method 
           110  receiving measurement signals 
           120  generating a sample signal by sampling received measurement signals 
           130  analyzing the sample signals 
           140  generating a switching signal 
         e error signal 
         B standby state 
         D conducting state 
         F flyback state 
         FG reference value 
         f SAMPLE  sampling frequency 
         f SW  switching frequency 
         H(T dist ) density function of the time intervals T dist    
         I L  output current 
         L inductance 
         P phase 
         PID Proportional-Integral-Differential 
         RG controlled variable 
         RS controlled system 
         S I  switch 
         S II  switch 
         SG correcting variable 
         SK circuit 
         SM measurement signal 
         S SAMPLE  sample signal 
         T dist  time interval between successive Line-contiguous trigger signals 
         TS trigger signal 
         U SOLL  setpoint voltage

Technology Category: 5