Patent ID: 12212240

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG.1schematically shows an exemplary system for carrying out the method in accordance with the invention for actuating a buck-boost converter TH. A buck-boost converter TH can convert an input voltage Ue into a regulated output voltage Ua, which is greater than, equal to, or less than the input voltage Ue. For this purpose, the buck-boost converter can be operated in dependence on a ratio between input voltage Ue and output voltage Ua in different modes, for example, in a buck converter mode and/or a mixed mode.

The buck-boost converter TH comprises for this purpose, for example, a buck converter, to which a boost converter is connected downstream. A circuit assembly for a buck-boost converter TH has, for example, an inductance or choke, which is used both by the buck converter part and also by the boost converter part of the buck-boost converter TH as an energy storage device. Furthermore, the buck-boost converter TH has in the power part, for example, two switching elements and two diodes, where within the buck converter part a first switching element as a buck converter switching element and a diode and within the boost converter part a second switching element as a boost converter switching element and a diode are used.

The two switching elements of the buck-boost converter TH are actuated by pulse-width-modulated and frequency-modulated control signals S1, S2using a common variable switching frequency.

A first control signal S1is used here for an actuation of the first switching element or the buck converter switching element and a second control signal S2is used for an actuation of the second switching element or the boost converter switching element. For a derivative of the pulse-width-modulated and frequency-modulated control signals S1, S2, a control loop for regulating the output voltage Ua, ist is set to a predeterminable target value Ua, soll, where the average current mode control is used as a regulating method, for example. For this purpose, a regulator unit RE is used, which is formed, for example, as a voltage regulator having a subordinate current regulation. Here, a mean current target value, for example, for a mean value of a current through the choke of the buck-boost converter, is predetermined to a subordinate current regulator by a voltage regulator, for example, based on a predeterminable target value Ua, soll and a present output voltage Ua, ist of the buck-boost converter TH. The current, for example, through the choke is then detected indirectly or directly by the subordinate current regulator and then a manipulated variable SG is generated, which is used to derive the pulse-width-modulated and frequency-modulated control signals S1, S2for switching or clocking the switching elements of the buck-boost converter TH.

Separate manipulated variables SG1, S22can then be derived via a unit for manipulated variable control SGS as a function of the input voltage Ue and output voltage Ua for each switching element of the buck-boost converter. In this case, for example, a first manipulated variable SG1for the first switching element or for a derivative of the first control signal S1and a second manipulated variable SG2for the second switching element or for a derivative of the second control signal S2can be ascertained from the manipulated variable SG provided by the regulator unit RE. One possible method for deriving these corresponding manipulated variables SG1, SG2is described, for example, in European patent application EP 20171701.4 (no prior publication).

Then, for example, a switching-off point in time of the respective switching element of the buck-boost converter TH is defined from the manipulated variable SG provided by the regulator unit RE or from the manipulated variables SG1, SG2derived therefrom. Thus, for example, the first manipulated variable SG1can specify a switching-off point in time for the first switching element or the buck converter switching element and the second manipulated variable SG2can specify a switching-off point in time for the second switching element or the boost converter switching element.

To derive the two pulse-width-modulated and frequency-modulated control signals S1, S2, in particular of the different switching-off points in time of the two switching elements, from the two manipulated variables SG1, S22, the different manipulated variables SG1, SG2are compared, for example, with the aid of comparator units C1, C2to a sawtooth signal CT1. For this sawtooth signal CT1, for example, an offset value CToffset is added to a sawtooth signal CT, which is generated by an oscillator unit OS (for example, a sawtooth generator). The two comparator units C1, C2supply two items of comparator signal information COMP1, COMP2, which are used by an actuation unit ANS to derive the pulse-width-modulated and frequency-modulated control signals S1, S2, above all for the switching-off points in time of the switching elements.

In order to be able to change the common switching frequency or be able to ascertain the switching-on point in time of the two switching elements for the control signals S1, S2, a minimum period duration Tmin and a maximum period duration Tmax are specified to the actuation unit ANS. The minimum period duration Tmin defines a maximum switching frequency, using which the switching elements are to be clocked. The minimum period duration Tmin can be selected, for example, based on a predeterminable efficiency of the buck-boost converter or predeterminable maximum interference emissions in a specific frequency range, in order to prevent excessively high switching losses and possibly excessively high interference emissions. The maximum period duration Tmax establishes a minimum switching frequency for clocking the switching elements and can be determined from a dynamic response of the control loop or the regulator unit RE, for example, to prevent instabilities of the regulator unit RE or in the control loop, which can occur above all if the variable switching frequency comes excessively close to a gain crossover frequency of the control loop.

Furthermore, for example, a recognition signal VAL for recognizing voltage minima of a voltage curve on the switching elements of the buck-boost converter TH is applied to the actuation unit ANS. The recognition signal VAL can be generated, for example, by a unit for monitoring the voltage curve on the switching elements of the buck-boost converter TH and for recognizing voltage minima or valleys in this voltage curve (a valley recognition unit VE). For this purpose, for example, a voltage measurement can be carried out on the switched off switching elements of the buck-boost converter TH. If a voltage minimum or valley is established by the voltage measurement in the voltage curve on the switched off switching elements, for example, then a pulse can thus be generated by the valley recognition unit VE.

Alternatively or additionally, a current curve through the inductance or choke of the buck-boost converter TH can also be monitored and the voltage minima or valleys in the voltage curve on the switching elements can be derived therefrom. A voltage minimum or valley is achieved with a positive zero crossing of the current through the inductance. As a result, a pulse can be generated by the valley recognition unit VE, for example, upon each positive zero crossing of the current through the inductance. The pulses are then passed on as the recognition signal VAL to the actuation unit ANS.

Furthermore, there is also the possibility that alternatively or additionally positive zero crossings of a voltage on an auxiliary winding of the inductance or choke of the buck-boost converter TH are evaluated, which signal points in time having horizontal slope in the current curve through the inductance or choke of the buck-boost converter TH, which each occur 90°, with respect to a valley oscillation period, before a voltage minimum or valley. The valley recognition unit VE has to insert a constant delay having the duration of 90° of a valley oscillation period in this case between a recognized positive zero crossing of the voltage on an auxiliary winding and the generation of a pulse on the recognition signal VAL.

The actuation unit ANS, above all with an analog implementation of the actuation unit ANS, for example, is possibly also provided the sawtooth signal CT generated by the oscillator unit OS, to define the limits of the variable switching frequency, i.e., maximum and minimum switching frequency, therefrom. With digital implementation variants of the actuation unit ANS, these limits can be implemented, for example, via counter units.

Furthermore, a setting signal DIS can be generated by the actuation unit ANS, by which the oscillator unit OS is reset at the switching-on point in time of the switching elements. That is, the sawtooth signal CT of the oscillator unit is set to zero and a new sawtooth CT or a new switching cycle is started.

Switching on and off of the two switching elements of the buck-boost converter TH, which is triggered by the control signals S1, S2, is performed, for example, by the actuation unit ANS in accordance with the method in accordance with the invention. An exemplary sequence of the method in accordance with the invention for actuating a buck-boost converter TH is schematically shown inFIG.2. This sequence can be performed, for example, using the system shown inFIG.1, in particular by the actuation unit ANS.

To determine the common switching-on point in time of the two switching elements of the buck-boost converter TH, in a monitoring step101, for example, the voltage curve on the two switching elements of the buck-boost converter TH is continuously ascertained and monitored by the valley recognition unit VE. For this purpose, for example, a voltage measurement can be performed on the two switching elements or the curve of the current through the inductance or choke of the buck-boost converter TH can be monitored or the voltage curve on an auxiliary winding of the inductance or choke of the buck-boost converter can be measured. The two switching elements are switched off in this case.

If, for example, in a recognition step102, a voltage minimum in the voltage curve on the switching elements (for example, due to voltage measurement or based on a positive zero crossing of the current through the choke) is recognized by the valley recognition unit VE, a pulse for the recognition signal VAL can thus be generated, for example, and passed on to the actuation unit ANS.

If a voltage minimum or valley is recognized, it is checked in a first checking step103whether the minimum period duration Tmin has been reached or exceeded. For this purpose, for example, the actuation unit ANS can check upon receiving a pulse of the recognition signal VAL whether the minimum period duration Tmin has been reached. If the minimum period duration Tmin has not yet been reached, in monitoring step101, the voltage curve on the two switching elements of the buck-boost converter TH is thus ascertained by the valley recognition unit VE and in recognition step102, a check is made for the recognition of a further voltage minimum or valley in the voltage curve on the switching elements. Upon recognition of a further voltage minimum, in first checking step103, reaching the minimum period duration Tmin is again checked.

If it is established in first checking step103upon recognition of a valley that the minimum period duration has been reached or exceeded, in a switching-on step104, the two switching elements of the buck-boost converter TH are thus switched on. For this purpose, for example, the two control signals S1, S2can be set by the actuation unit ANS and simultaneously the setting signal DIS for the oscillator unit OS can be generated, to reset the oscillator unit OS or the sawtooth signal CT. With switching-on step104or the switching-on of the two switching elements of the buck-boost converter TH, a new switching cycle is started and the switching frequency for clocking the switching elements is varied.

In a switching-off step105, the two switching elements are then switched off in accordance with the desired switching-on times. The switching-off point in time of the respective switching element of the buck-boost converter is predetermined, for example, by the respective manipulated variable SG1, SG2, which was derived from the manipulated variable SG provided by the regulator unit RE for regulating the output voltage Ua. Based on the respective manipulated variables SG1, SG2, a respective item of comparator signal information COMP1, COMP2is created for the respective switching elements, for example, via comparator units C1, C2. Based on this comparator signal information COMP1, COMP2, the respective control signal S1, S2is then reset, for example, by the actuation unit ANS, to switch off the associated switching element. In a buck-boost converter TH, which is operated in the mixed mode, where the boost converter switching element is typically switched off first here and then the buck converter switching element. In a buck converter mode of the buck-boost converter TH, only the buck converter switching element or the first switching element is clocked, while the boost converter switching element or the second switching element remains switched off.

If, for example, no voltage minimum in the voltage curve on the switching elements (for example, by voltage measurement or based on a positive zero crossing of the current through the choke) is recognized by the valley recognition unit VE in recognition step102, in a second checking step106, which can be performed, for example, in particular after reaching the minimum period duration Tmin, for example, by the actuation unit ANS, it is checked whether the maximum period duration Tmax has passed. As long as the maximum period duration Tmax has not yet been reached, the voltage curve on the two switching elements of the buck-boost converter TH is still ascertained in monitoring step101by the valley recognition unit VE and the recognition of a further voltage minimum or valley in the voltage curve on the switching elements is checked in recognition step102. If no voltage minimum or valley is recognized up to the passage of the maximum period duration Tmax, switching-on step104is thus carried out. That is, the switching elements, even without recognized voltage minimum in the voltage curve on the switching elements, are switched on “hard” so as not to fall below a minimum switching frequency and to start a new switching cycle. Furthermore, the setting signal DIS for the oscillator unit OS for resetting the sawtooth signal CT is also generated and sent to the oscillator unit. The switching elements of the buck-boost converter TH are then switched off again according to switching-off step105and the respective switching-off points in time.

If, after switching-off step105, both switching elements of the buck-boost converter are switched off, the method can be started again with monitoring step101to determine the next optimum switching-on point in time, i.e., switching-on the two switching elements at a voltage minimum or valley, for the control signals S1, S2and to start the next switching cycle.

An implementation of the method in accordance with the invention or the actuation unit ANS for the actuation of the switching elements or the generation of the control signals S1, S2can occur in an analog manner, for example, with the aid of comparators and reset-set or RS flip-flops. Corresponding voltage and signal curves for these analog implementation variants are shown by way of example inFIG.3a.

FIG.3ashows here, in a signal curve CT, a time curve of the sawtooth signal CT, which is generated by the oscillator unit OS. In the first signal curve, a maximum value CTmax for the sawtooth signal CT is plotted, by which the maximum period duration Tmax is predetermined.

The shifted sawtooth signal CT1, which is shown by way of example in a signal curve CT1, is derived from the sawtooth signal CT by addition of an offset value CToffset. The shifted sawtooth signal CT1is compared, for example, by the comparator units C1, C2, to the manipulated variables SG1, SG2plotted in the second signal curve. The first manipulated variable SG1is assigned to the first switching element or the buck converter switching element. The second manipulated variable SG2is assigned to the second switching element or the boost converter switching element. The respective switching-off points in time of the two switching elements are derived from a comparison of the shifted sawtooth signal CT1to the two manipulated variables SG1, SG2.

The comparison of the shifted sawtooth signal CT1to the first manipulated variable SG1, for example, by a comparator unit C1, supplies a first item of comparator signal information COMP1, which is shown in the signal curve COMP1and from which via the actuation unit ANS, the switching-off point in time of the first switching element or the buck converter switching element for the first pulse-width-modulated and frequency-modulated control signal S1is determined. An exemplary curve of the first control signal S1for the buck converter switching element is shown here as signal curve S1. If the shifted sawtooth signal CT1exceeds the first manipulated variable SG1, for example, via a comparator unit C1, the first item of comparator signal information COMP1is thus set and the first control signal S1is reset, by which the buck converter switching element is switched off.

Similarly, the comparison of the shifted sawtooth signal CT1to the second manipulated variable SG2, for example, via the comparator unit C2, supplies the switching-off point in time for the second switching element or the boost converter switching element. For this purpose, a second item of comparator signal information COMP2is ascertained from the comparison, which is shown in the signal curve COMP2. From the second item of comparator signal information COMP2the switching-off point in time of the boost converter switching element is then ascertained by the actuation unit ANS for the second pulse-width-modulated and frequency-modulated control signal S2(shown in the signal curve S2). If the shifted sawtooth signal CT1exceeds the second manipulated variable SG2, for example, via a comparator unit C2, the second item of comparator signal information COMP2is thus set and the second control signal S2is reset, by which the boost converter switching element is switched off. If, for example, the second manipulated variable SG2is less than the offset value CToffset, the boost converter switching element is then not clocked, but rather remains switched off, i.e., the buck-boost converter TH operates in the buck converter mode.

In a signal curve VAL, the recognition signal VAL is shown by way of example, which is generated by the valley recognition unit VE. Each pulse of the illustrated signal curve VAL corresponds here to a recognized voltage minimum or valley in the voltage curve on the switching elements of the buck-boost converter TH. The pulses have, for example, a defined amplitude AVALand a defined pulse width TVAL. The amplitude AVALcan be defined here, for example, such that the maximum switching frequency and thus the minimum period duration Tmin is ascertainable from a ratio of the amplitude AVALto the maximum value CTmax. That is, the maximum switching frequency, which is determined by the predetermined minimum period duration Tmin, can be predetermined by corresponding definition of the amplitude AVALof the pulses of the recognition signal VAL.

The recognition signal VAL is evaluated, for example, by the actuation unit ANS. For this purpose, for example, a sum signal CT2(shown in the signal curve CT2) is formed from the sawtooth signal CT and the recognition signal VAL. This sum signal CT2is then compared, for example, via a comparator unit by the actuation unit ANS to the maximum value CTmax. If the maximum value CTmax is exceeded by the sum signal CT2, then a setting signal DIS is triggered, which has a width TDISand is shown in a signal curve DIS.

Furthermore, the oscillator unit OS or the sawtooth signal CT of the oscillator unit OS is reset by the setting signal DIS. The two items of comparator signal information COMP1, COMP2thus also tilt back again and, for example, the control signals S1, S2of the switching elements of the buck-boost converter are set via RS flip-flops and thus a new switching cycle is started. That is, the two switching elements are switched on simultaneously.

Alternatively, the actuation method in accordance with the invention, in particular the actuation unit ANS, can also be digitally implemented. For this purpose, for example, a microcontroller, a programmable logic device (PLC), or other digital components can be used. Voltage and signal curves for a digital implementation variant, for example, via a programmable logic device (PLD) are shown by way of example inFIG.3b.

With a digital implementation of the actuation unit ANS, the limiting of the switching frequency or the checking of the predetermined minimum and maximum period duration can be implemented, for example, via a counter unit HZ. Furthermore, a counter unit DIS-Z can likewise be used for the implementation of the defined width of the setting signal DIS. InFIG.3b, the graphic representations of the counter units HZ, DIS-Z are shown by way of example in the curves HZ, DIS-Z.

The curve HZ shows, for example, a graphic representation of the counter unit HZ, which overflows at a predetermined maximum value Tmax fix. This maximum value corresponds to the predetermined maximum period duration Tmax, by which the minimum switching frequency can be defined. Furthermore, the minimum period duration Tmin is plotted in the curve HZ, which establishes the maximum switching frequency and is not to be fallen below.

An exemplary curve of the recognition signal VAL, which is generated by the valley recognition unit VE, is again shown in the signal curve VAL. The positive flanks of the pulses of the signal curve VAL again indicate recognized voltage minima or valleys in the voltage curve on the switching elements of the buck-boost converter TH. If a rising flank of a pulse of the recognition signal VAL falls in an area of the counter curve HZ between the limits Tmin and Tmax, then the counter unit HZ is thus reset and the setting signal DIS, shown in the signal curve DIS, is generated and the counter unit DIS-Z (graphically represented in the curve DIS-Z) is triggered. The counter unit DIS-Z has, for example, an overflow value DISMAX, by which the pulse width TDISis defined.

Furthermore, the oscillator unit OS or the sawtooth signal CT of the oscillator unit OS is reset by the setting signal DIS, by which the two items of comparator signal information COMP1, COMP2also tilt back again. The two pulse-width-modulated and frequency-modulated control signals S1, S2are thus set. These are shown in the corresponding signal curves S1, S2, COMP1, COMP2. The two switching elements of the buck-boost converter TH are switched on by the setting of the control signals S1, S2and a new switching cycle is started.

Furthermore, the signal curve CT1of the shifted sawtooth signal CT1is again shown inFIG.3b, which is generated from the sawtooth signal CT of the oscillator unit OC shifted by the offset value CToffset. The switching-off points in time for the two switching elements are derived with the aid of the first and second manipulated variable SG1, SG2from the sawtooth signal CT1, as already described in the signal curves inFIG.3a.

With the aid of the actuation method according to the invention, in a simple manner, the two pulse-width-modulated and frequency-modulated control signals S1, S2are always set at the same point in time and thus the switching elements are switched on at a common switching-on point in time. Due to the different manipulated variables SG1, ST2for the two switching elements, the two pulse-width-modulated and frequency-modulated control signals can be reset at different switching-off points in time. In addition, it is possible that the boost converter switching element remains constantly switched off or the associated second control signal S2remains constantly reset if the second manipulated variable SG2for the boost converter switching element is less than the offset value CToffset. That is, only the first switching element or the buck converter switching element is clocked and the buck-boost converter TH is operated in the buck converter mode.

Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and illustrated may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.