Device and method for providing an actuation signal for a pulse-width modulation, converter, and electric drive system

Abstract

The invention relates to the process of producing actuation pulses for a pulse-width-modulated actuation process. Instead of centered pulses, pulses are produced which are shifted to the edge of a pulse period. In this manner, the requirement for a minimum pulse-width between two switching processes can be better met.

Description

[0001] Description

[0002] title

[0003] Device and method for providing a control signal for a pulse width modulation, power converter and electric drive system

[0004] Technical area

[0005] The present invention relates to a device and a method for providing a control signal for pulse width modulation, an electrical power converter and an electrical drive system with such a power converter.

[0006] State of the art

[0007] Electrical power converters, especially inverters, typically comprise power electronic components with semiconductor switching elements. By selectively opening and closing these semiconductor switching elements, an AC voltage with a desired amplitude and frequency can be generated from a supplied DC voltage. For this purpose, the semiconductor switching elements are usually controlled using pulse-width modulated (PWM) control signals.

[0008] The document DE 10 2016 220 892 A1, for example, discloses a method for controlling a power converter by means of space vector pulse width modulation, wherein a control method is proposed which is intended to reduce the number of switching operations.

[0009] With such pulse-width modulated control methods, a minimum pulse width must be observed, which specifies a time that must be maintained between two switching operations.

[0010] Disclosure of the Invention The present invention provides a device and a method for providing a control signal for pulse width modulation, an electrical power converter, and an electrical drive system having the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0011] Accordingly, it is provided:

[0012] A device for providing a control signal for pulse width modulation. The control signal comprises a sequence of pulse periods with a predetermined period. The device is designed to determine a pulse width for the control signal of the pulse width modulation. Furthermore, the device is designed to generate a center-centered pulse with the determined pulse width if the determined pulse width is less than a period of the control signal less a predetermined minimum duration. Furthermore, the device is designed to generate a pulse whose temporal position within the pulse period deviates from a center-centered pulse if the determined pulse width is greater than the period of the control signal less the predetermined minimum duration.

[0013] Furthermore, it is planned:

[0014] An electrical power converter comprising at least one half-bridge, a driver stage, and a device according to the invention for providing a control signal for pulse-width modulation. The at least one half-bridge is designed to be connected to a DC voltage source on the input side. Furthermore, the at least one half-bridge comprises two semiconductor switching elements connected in series. The driver stage is designed to control the switching elements of the at least one half-bridge using the pulses provided by the device for generating a control signal.

[0015] Furthermore, an electric drive system comprising an electric machine and an electric power converter according to the invention is provided. The electric power converter is designed to supply the electric machine on the output side.

[0016] Finally, it is planned:

[0017] A method for providing a control signal for pulse width modulation. The control signal comprises a sequence of pulse periods with a predetermined period duration. The method comprises a step for determining a pulse width of the control signal for the pulse width modulation. The method further comprises a step for generating a center-centered pulse with the determined pulse width if the determined pulse width is less than or equal to the period duration of the control signal minus a predetermined minimum duration. Finally, the method comprises a step for generating a pulse whose temporal position within the pulse period deviates from a center-centered pulse if the determined pulse width is greater than the period duration of the control signal minus the predetermined minimum duration.

[0018] Advantages of the invention

[0019] The present invention is based on the finding that when switching semiconductor switching elements on and off, a predetermined minimum switching duration must be maintained between two switching operations. For example, if such semiconductor switching elements are controlled by pulse-width modulation, the duty cycle of such a pulse-width modulation cannot be fully utilized from 0 to 100 percent without violating this minimum pulse width requirement. Therefore, pulse-width modulation is only possible for a range of duty cycles where the minimum pulse width between two consecutive pulses can be maintained.

[0020] Therefore, one idea of ​​the present invention is to take this finding into account and to create a device and a method for providing control signals for pulse-width modulation, which enables pulse-width modulation over the widest possible range of duty cycles. Furthermore, the transition between pulse-width modulated control and the permanent control state is to be improved.

[0021] For this purpose, for example, pulse-width modulation with center-centered pulses of a given duty cycle can be generated for as long as possible while maintaining the required minimum pulse width. Furthermore, for duty cycles below 100 percent, where center-centered pulses would violate the minimum pulse width requirements, a pulse shifted to the beginning or end of the pulse period is generated.

[0022] In this way, it is possible to realize the pulse-width modulated control of semiconductor switching elements over a wider range of the duty cycle without having to violate the required minimum pulse width.

[0023] By shifting the pulse width within the pulse period, it is possible to adjust the switching times in such a way that, especially in conjunction with preceding or following pulses, the minimum pulse width requirements can still be met even with very large duty cycles. For example, if a current pulse is followed by another pulse with a duty cycle of 100 percent, i.e., continuous control throughout the entire pulse period, the current pulse can be shifted to the end of the pulse period. This way, no switching operation is required between the end of the current pulse and the subsequent pulse. Accordingly, the minimum pulse width requirement cannot be violated.Similarly, following a pulse period with full control, i.e., a duty cycle of 100 percent, a subsequent pulse can be shifted such that, here too, no switching operation is required between the pulse with a duty cycle of 100 percent and the subsequent pulse. Accordingly, the full off-time is shifted to the end of such a pulse period, which also makes it easier to meet the minimum pulse width requirements. A pulse period is defined here as a complete interval of the control signal with the period duration of the pulse width modulation. The pulse period thus corresponds to a section of a control signal with the period duration of the pulse width modulation.If a time grid with this period duration is used to form the control signal for the pulse width modulation, one pulse period corresponds to a section of the control signal between two grid points of this time grid.

[0024] The pulse width refers to the duration of a pulse within the pulse period. The duty cycle is thus calculated from the quotient of the pulse width divided by the pulse period. A centered pulse is a pulse positioned within the pulse period such that the time span from the beginning to the first switching edge is exactly as long as the time span from the second switching edge to the end of the pulse period. In other words, the time from the beginning of the pulse period to the first edge of the pulse is exactly as long as the time span from the second edge of the pulse to the end of the pulse period.

[0025] According to one embodiment, the specified minimum duration corresponds to the minimum pulse width for controlling a power electronic component. For example, the minimum duration can be assumed to be a minimum pulse width that corresponds to the time interval between two consecutive switching operations of a semiconductor switch. This minimum pulse width can, for example, correspond to the time interval between a switch-on operation and a switch-off operation, or between a switch-off operation and a switch-on operation of a semiconductor switch.

[0026] According to one embodiment, the device for providing the control signal is designed to generate a pulse whose beginning coincides with the beginning of a pulse period if the determined pulse width is greater than a period of the control signal minus the predetermined minimum duration. Furthermore, the device can also generate a pulse whose end coincides with the end of the pulse period if the determined pulse width is greater than a period of the control signal minus the predetermined minimum duration. In this way, a generated pulse is shifted either to the beginning or the end of the pulse period if, in the case of a center-centered pulse with the same pulse width, less than half of the minimum pulse width would remain at the beginning and end.

[0027] According to one embodiment, the device for providing the control signal is designed to generate a pulse whose beginning corresponds to a center-centered pulse with the determined pulse width and whose pulse duration is extended until the end of the pulse period if the determined pulse width is greater than a period duration of the control signal less the predetermined minimum duration if a subsequent pulse has a duty cycle of 100 percent. In other words, an originally center-centered pulse is extended until the end of the pulse period if the subsequent pulse has a duty cycle of 100 percent, i.e., corresponds to control over the entire pulse period. This avoids a switching operation at the end. Consequently, the requirement for the minimum pulse width cannot be violated.

[0028] According to one embodiment, the device for providing the control signal is designed to generate a pulse whose beginning corresponds to a centered pulse with the determined pulse width and whose pulse duration is extended until the end of the pulse period if the determined pulse width is greater than a predetermined threshold value and the determined pulse width is greater than the pulse width of an immediately preceding pulse. If the pulse width of a current pulse is greater than the pulse width of a previous pulse, it can be assumed that the pulse width will also increase in the subsequent pulse. Thus, for example, a threshold value can be set such that if the threshold value for the pulse width is exceeded, the predetermined minimum pulse width can no longer be maintained. Therefore, subsequent pulses are expected to have a duty cycle of 100 percent.For the transition, the current pulse can therefore be extended to the end, so that no switch-off process is required and the minimum pulse width requirements are not violated. According to one embodiment, the device for providing a control signal is designed to generate a pulse whose start corresponds to the start of the pulse period and whose pulse duration corresponds to the determined pulse width if a previous pulse has a duty cycle of 100 percent. In this way, during the transition from full control with a duty cycle of 100 percent to smaller duty cycles, the pulse can initially be shifted to the start of the pulse period. This leaves a longer period at the end of the pulse period, which makes it possible to comply with the minimum pulse width requirement even at high duty cycles.

[0029] The above embodiments and further developments can be combined with one another as desired, where appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0030] Short description of the drawings

[0031] Further features and advantages of the invention are explained below with reference to the figures. These show:

[0032] Fig. 1: a schematic block diagram of an electric drive system with a power converter according to an embodiment;

[0033] Fig. 2: a schematic representation of a pulse for a pulse width modulated control;

[0034] Fig. 3: a diagram illustrating the principle for providing the control pulses according to an embodiment; and

[0035] Fig. 4: a flowchart underlying a method for providing control signals according to one embodiment. Description of Embodiments

[0036] Figure 1 shows a schematic block diagram of an electric drive system according to one embodiment. A DC voltage source 4 can provide a DC voltage at the input of an electric power converter 3. This provided DC voltage can be converted by the power converter 3 into a single-phase or multi-phase AC voltage, which is provided to an electric machine 5. In this case, the electric power converter 3 can comprise power electronic components, for example so-called B2 bridges. In particular, a B2 bridge can be provided for each phase of an AC voltage provided on the output side. Thus, for a three-phase AC voltage, three B2 bridges can be combined to form a so-called B6 bridge. Each B2 bridge comprises two switching elements M1 to M6 connected in series. The upper switching elements M1, M3 and M5 are controlled complementarily to the lower switching elements M2, M4 and M6.Furthermore, a dead time can be provided between the switching off of the upper or lower switching elements and the switching on of the complementary switching elements. In this way, for example, a short circuit caused by delayed switching behavior or similar can be avoided.

[0037] The switching signals required to control the switching elements M1 to M6 can be generated by a device 1 for providing control signals. These generated control signals can be amplified by a driver stage 2 to provide the required switching power for controlling the switching elements M1 to M6.

[0038] To generate the alternating voltage by the power converter 3, the switching elements M1 to M6 can be controlled in particular by pulse-width modulation. For example, the duty cycle of this pulse-width modulated control can be determined using a setpoint specification or similar. Since this step can be carried out in a known, conventional manner, it will not be discussed in detail here. Figure 2 shows a schematic diagram illustrating the basic principle of pulse-width modulated control. For pulse-width modulated control, pulses with a predetermined period T are generated. In principle, a fixed period T and a corresponding fixed frequency can be used. However, it is also possible to vary the period T or the corresponding frequency during operation.

[0039] During each period T, a pulse P is generated. For example, at time t1 the pulse can change from logical zero to logical one, and at time t2 the pulse can change from logical one to logical zero. Thus, from the beginning at time t1 to time t2 the pulse is at logical zero, from t1 to t2 the pulse is at logical one and then from t2 to the end of the pulse at t2 the pulse is back at logical zero. In particular, such a pulse P can be generated as a center-centered pulse, so that the time span from t1 to the middle of the pulse at T / 2 is exactly as long as the time from the middle of the pulse at T / 2 to the switch-off time t2 of the pulse P. This results in a switch-on time t_on of t2 - t1. From this, a duty cycle of the pulse P to t_on / T is calculated.

[0040] To control a half-bridge of the power converter 3 shown in Figure 1, for example, an upper switching element M1 can be controlled according to a pulse-width modulated signal generated in this way, while the corresponding lower switching element M2 is controlled with the inverse signal.

[0041] When controlling the switching elements M1 to M6, it is important to note that a specified minimum pulse width t_min must be maintained between two consecutive switching operations, i.e. an on-operation followed by an off-operation, or an off-operation followed by an on-operation. As the duty cycle increases, however, it is possible that the time span from the switch-off time t2 of a pulse to the switch-on time ti of a subsequent pulse is shorter than this specified minimum pulse width t_min. In this case, switching is no longer possible, and the corresponding switching elements are switched on or off for the entire period T. This corresponds to a duty cycle of 100 percent. Consequently, depending on the selection of the period T and the specified minimum pulse width, the pulse width modulation can only be continuously adjusted down to a duty cycle of less than 100 percent.Subsequently, by specifying the minimum pulse width, a jump to the duty cycle of 100 percent occurs.

[0042] Figure 3 shows a schematic representation of a switching pattern sequence for generating control signals for a pulse-width modulated control according to one embodiment. Sections I and II each show a center-centered pulse, with the duty cycle being so low that the minimum pulse width requirement can be met between the pulses. Subsequently, the duty cycle is to be further increased for periods III and IV so that a duty cycle of 100 percent is achieved in period IV. However, this would result in the switch-off in period III occurring so late during the transition from period III to period IV that the minimum pulse width requirement would be violated. The duty cycle of 90% shown in Section II is only an example.The extension or postponement of the pulse until the end of the period depends in particular on the minimum pulse width.

[0043] Therefore, according to the invention, no switch-off process is provided in the pulse in period III. Accordingly, the pulse in period III transitions directly into the pulse in period IV. To achieve this, for example, the pulse in period III can simply be extended until the end of the period. Alternatively, it is also possible to delay the switch-on time in period III until the resulting pulse has the originally desired duty cycle. In other words, a right-aligned pulse with the desired duty cycle is generated. The required switch-off time is shifted entirely to the beginning of the pulse.

[0044] The following pulse IV has, as already explained, a duty cycle of

[0045] 100 percent, meaning no switching process occurs during this pulse, especially no change to logic zero. This state can also extend over several periods.

[0046] If a change from a duty cycle of 100 percent to a lower duty cycle is required, a pulse can be generated, as shown in Period V, that begins with a logic one and whose logic zero component is shifted entirely to the end. This creates a left-aligned pulse with the desired duty cycle. In particular, this also results in a longer off-time at the end of such a pulse, so that the required minimum pulse width can also be achieved for the transition to subsequent pulses in Period VI.

[0047] In summary, for rising sequences, i.e., pulse sequences with an increasing duty cycle, a right-aligned pulse is generated during the transition to sustained sequences, i.e., pulses with a duty cycle of 100 percent. A left-aligned pulse is generated during the transition from sustained sequences to falling sequences with a continuously decreasing duty cycle.

[0048] Although the present method has been described in the context of pulses in which a transition from logic zero to logic one occurs at the beginning and a transition from logic one to logic zero occurs at the end, the inventive principle can also be applied to complementary pulses in which a transition from logic one to logic zero occurs first and then a transition from logic zero to logic one occurs.

[0049] Figure 4 shows a flowchart underlying a method for providing control pulses for pulse width modulation. In step S1, a pulse width for a control signal of the pulse width modulation is first determined. If the requirements for the minimum pulse width are met, for example, the period of the control signal minus a predetermined minimum duration is less than or at least equal to the determined pulse width, a center-centered pulse is generated in step S2. If the determined pulse width is greater than the period of the control signal minus the predetermined minimum duration, a pulse is generated whose temporal position within a section with the period of the pulse width modulation deviates from a center-centered pulse.

[0050] In particular, as previously described, a right-aligned pulse can be formed during the transition from a rising sequence, i.e., a period with an increasing duty cycle, to a holding sequence, i.e., a period with a duty cycle of 100 percent. Furthermore, a left-aligned pulse can initially be formed during the transition from a holding sequence to a falling sequence, i.e., a sequence with decreasing duty cycles of consecutive periods.

[0051] For example, to generate the right- or left-aligned pulses, a pulse with the specified duty cycle can be generated. Alternatively, it is also possible to use a center-centered pulse with the desired duty cycle and extend such a pulse at the beginning or end until the beginning or end of the period, respectively.

[0052] In summary, the present invention relates to the generation of drive pulses for pulse-width modulated control. Instead of center-centered pulses, pulses can be generated that are shifted to the edge of a section with the period of the pulse-width modulation. In this way, the requirements for a minimum pulse width between two switching operations can be better met.

Claims

Claims 1. Device (1) for providing a control signal for pulse width modulation, wherein the control signal comprises a sequence of pulse periods with a predetermined period (T) and the device (1) is designed to determine a pulse width (t_on) for the control signal of the pulse width modulation; to generate a center-centered pulse with the determined pulse width (t_on) if the determined pulse width (t_on) is less than the period (T) of the control signal less a predetermined minimum period, and to generate a pulse whose temporal position within the pulse period differs from a center-centered pulse if the determined pulse width (t_on) is greater than the period (T) of the control signal less the predetermined minimum period.

2. Device (1) according to claim 1, wherein the specified minimum duration is a minimum pulse width for controlling a power electronic component.

3. Device (1) according to claim 1 or 2, wherein the device (1) is designed to generate a pulse whose start coincides with the beginning (ta) of a pulse period and / or whose end coincides with the end (te) of the pulse period if the determined pulse width (t_on) is greater than the period (T) of the control signal less the specified minimum duration.

4. Device (1) according to claim 1 or 2, wherein the device (1) is designed to generate a pulse whose beginning corresponds to a center-centered pulse with the determined pulse width and whose pulse duration is extended or shifted until the end of the pulse period. The device (1) according to claim 1 or 2, wherein the device (1) is designed to generate a pulse whose start corresponds to a center-centered pulse with the determined pulse width and whose pulse duration is extended or shifted to the end (Te) of the pulse period if the determined pulse width (t_on) is greater than a predetermined threshold and the determined pulse width (t_on) is greater than the pulse width of an immediately preceding pulse.Device (1) according to claim 1 or 2, wherein the device (1) is designed to generate a pulse whose start corresponds to the start (ta) of the pulse period and whose pulse duration corresponds to the determined pulse width (t_on) if a preceding pulse has a duty cycle of 100 percent. Electrical power converter comprising: at least one half-bridge designed to be connected on the input side to a DC voltage source (4); a device (1) for providing a control signal for pulse width modulation according to any one of claims 1 to 6; and a driver stage (2) designed to control switching elements (M1-M6) of the at least one half-bridge using the pulses generated by the device (1) to provide the control signal. Electrical drive system comprising: an electric machine (5); and. an electrical power converter according to claim 7, wherein the electrical power converter is designed to supply the electrical machine (5) on the output side. A method for providing a control signal for pulse width modulation, wherein the control signal comprises a sequence of pulse periods with a predetermined period (T) and the method comprises the following steps: Determining (Sl) a pulse width (t_on) of the control signal for pulse width modulation; Generating (S2) a center-centered pulse with the determined pulse width (t_on) if the determined pulse width (t_on) is smaller than a period (T) of the control signal minus a specified minimum duration, and Generating (S3) a pulse whose temporal position within the pulse period differs from a center-centered pulse if the determined pulse width (t_on) is greater than the period (T) of the control signal minus the specified minimum duration.

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