Modular braking adjuster with hybrid design

Abstract

A modular braking adjuster includes a brake resistor and at least two sub-modules arranged in series. At least one sub-module is constructed as a full-bridge module and at least one sub-module is constructed as a double half-bridge module. A control device is configured to generate a voltage across the serially connected sub-modules, wherein the voltage has a direct voltage component and an alternating voltage component. The control device provides open-loop or closed-loop control of the alternating voltage component, such that the alternating voltage component is at least temporarily greater than the direct voltage component and the time-averaged energy taken up by the modular braking adjuster is converted into heat in the brake resistor. An electric drive having the modular braking adjuster and a power converter electrically connected on the direct voltage side to the modular braking adjuster and a method for operating a modular braking adjuster are also disclosed.

Claims

1. A modular braking adjuster, comprising: a brake resistor and at least two submodules, wherein the brake resistor and the at least two submodules are connected to form a series circuit, wherein at least one submodule is constructed as a full-bridge module and at least one submodule is embodied as a double half-bridge module, and a control device configured to generate a voltage across the serially connected submodules, with the voltage composed of a direct voltage component and an alternating voltage component, to control with the direct voltage component by open-loop control or closed-loop control power to be converted into heat by the modular braking adjuster, to control an amplitude of the alternating voltage component by open-loop control or closed-loop control in such a way that the energy taken up by the modular braking adjuster averaged over time is converted into heat in the brake resistor, wherein the amplitude of the alternating voltage component is at least temporarily greater than the direct voltage component, and to at least temporarily generate a negative proportion of the current through the modular braking adjuster for maintaining an energy balance.

2. The modular braking adjuster of claim 1, wherein the alternating voltage component has a periodic curve and an average value of zero.

3. The modular braking adjuster of claim 1, wherein at least one of the at least two submodules has a bypass switch configured to short-circuit terminals of the at least one submodule.

4. The modular braking adjuster of claim 1, wherein all of the at least two submodules have a bypass switch configured to short-circuit terminals of the submodules.

5. An electric drive, comprising: a modular braking adjuster as set forth in claim 1; and a power converter electrically connected on a direct voltage side to the modular braking adjuster.

6. The electric drive of claim 5, wherein the power converter is constructed as a modular multilevel power converter.

7. A method for operating an electric drive as set forth in claim 5, the method comprising: generating with the submodules a voltage across the serially connected submodules, which, at least temporarily, comprise a negative and a positive voltage range, wherein the voltage comprises a direct voltage component providing open-loop or closed-loop control of the power to be converted into heat by the modular braking adjuster and an alternating voltage component, wherein the alternating voltage component is controlled by open-loop control or closed-loop control such that the energy taken up by the modular braking adjuster averaged over time is converted into heat in the brake resistor, wherein an amplitude of the alternating voltage component is at least temporarily greater than the direct voltage component, and generating at least temporarily with the modular braking adjuster a negative proportion of the current for maintaining an energy balance.

8. The method of claim 7, wherein the alternating voltage component has a periodic curve and an average value of zero.

9. A method for operating a modular braking adjuster as set forth in claim 6, the method comprising: generating with the submodules a voltage across the serially connected submodules, which, at least temporarily, comprise a negative and a positive voltage range, wherein the voltage comprises a direct voltage component providing open-loop or closed-loop control of the power to be converted into heat by the modular braking adjuster and an alternating voltage component, wherein the alternating voltage component is controlled by open-loop control or closed-loop control such that the energy taken up by the modular braking adjuster averaged over time is converted into heat in the brake resistor, wherein an amplitude of the alternating voltage component is at least temporarily greater than the direct voltage component, and generating at least temporarily with the modular braking adjuster a negative proportion of the current for maintaining an energy balance.

10. The method of claim 9, wherein the alternating voltage component has a periodic curve and an average value of zero.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention is described and explained in detail below with reference to the exemplary embodiments depicted in the figures, which show:

(2) FIG. 1 and FIG. 2 exemplary embodiments of the modular braking adjuster,

(3) FIG. 3 a submodule as a full-bridge module,

(4) FIG. 4 a submodule as a double half-bridge module,

(5) FIG. 5 and FIG. 6 exemplary embodiments of proposed electric drives,

(6) FIG. 7 time curves of electrical variables, and

(7) FIG. 8 working areas of the modular braking adjuster.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(8) FIG. 1 shows a modular braking adjuster 1. This has a series circuit 4 of at least two submodules 2 and a brake resistor 3. Herein, the series circuit 4 also comprises a series circuit of the submodules 2. With respect to the submodules 2, at least one submodule 2 is embodied as a full-bridge module 21 and one submodule 2 is embodied as a double half-bridge module 22. The modular braking adjuster can also have a plurality of submodules 2, as shown in FIG. 2. Herein, the submodules 2 can be full-bridge modules 21 and double half-bridge modules 22. However, the use of all other known submodules 2 is also possible. The modular braking adjuster 1 is configured to be connected at its terminals 11 to a DC link 9 of a power converter 5, 51.

(9) A voltage u.sub.BR can be generated across the series circuit of the submodules 2. The voltage u.sub.BR enables a current i.sub.BR to be generated through the modular braking adjuster 1. The current through the brake resistor 3 causes the electrical energy to be converted into heat. The operating voltage Up is applied across the modular braking adjuster 1. If the modular braking adjuster 1 is connected to the DC link of a power converter, the DC link voltage is applied to the modular braking adjuster. In this case, the modular braking adjuster 1 is said to be connected to the direct voltage side of the power converter.

(10) FIGS. 3 and 4 show exemplary embodiments of submodules 2. Herein, FIG. 3 shows a full-bridge module 21 and FIG. 4 a double half-bridge module. These are part of the proposed design. In addition, the modular braking adjuster 1 can be extended with submodules 2 that are already known. To avoid repetition, reference is made to the description of FIGS. 1 and 2 and to the reference symbols introduced there.

(11) The depicted exemplary embodiments of the submodules 2, 21, 22 comprise four semiconductor switches and at least one capacitor. Switching the semiconductor switches enables an output voltage U.sub.sub to be generated at the terminals of submodule 2. Herein, a trigger circuit transmits the trigger signals to the semiconductor switches of submodule 2. A bypass switch 6 can optionally be provided in submodule 2 to bypass the corresponding submodule 2.

(12) FIG. 3 shows a so-called full-bridge module. This has four semiconductor switches and a capacitor. The voltage U.sub.C.sub is applied to the capacitor. By switching operations of the semiconductor switches, the output voltage U.sub.sub at the terminals 11 of submodule 2 can be generated as zero, the positive or negative capacitor voltage U.sub.C.sub.

(13) FIG. 4 shows a so-called double bridge module. This has four semiconductor switches and two capacitors. The voltage U.sub.C1,sub or U.sub.C2,sub is applied to the capacitors in each case. By switching operations of the semiconductor switches, the output voltage U.sub.sub at the terminals 11 of submodule 2 can be generated as zero, one of the capacitor voltages U.sub.C1,sub, U.sub.C2,sub, or the sum of the capacitor voltages U.sub.C1,sub, U.sub.C2,sub.

(14) FIG. 5 depicts an exemplary embodiment of an electric drive 10. Herein, an electric device 7 is electrically connected to the alternating voltage side of a power converter 5. The modular braking adjuster 1 is connected to the direct voltage side of the power converter 5 via the DC link 9. The electric device 7 can, for example, be a power supply network or an electric machine.

(15) FIG. 6 shows an electric drive 10 in which the power converter 5 is embodied as a modular multilevel power converter 51. The modular braking adjuster 1 and the modular multilevel power converter 51 are connected to one another via the DC link 9 to which the voltage U.sub.D is applied. Herein, the modular multilevel power converter 51 may, but does not necessarily, have as submodules 2 the same submodules 2, i.e., full-bridge modules 21 and/or double half-bridge modules 22, as the modular braking adjuster 1. Moreover, the series circuit of the submodules 2 of the modular multilevel power converter 51 also has an inductance 8, which improves the closed-loop control behavior of the modular multilevel power converter 51. The terminals L1, L2, L3 represent the terminals on the alternating voltage side or, in short, the alternating voltage side of the modular multilevel power converter 51. In this exemplary embodiment, the modular multilevel power converter 51 has a three-phase embodiment. Alternatively, a single-phase embodiment with a neutral conductor or also any number of phases is also possible by providing a corresponding number of phase modules in the modular multilevel power converter 51.

(16) FIG. 7 shows a typical time curve of the voltage u.sub.BR across the series circuit of the submodules 2 and the associated current i.sub.BR through the modular braking adjuster 1. To avoid repetition, reference is made to the description of FIGS. 1 to 6 and to the reference symbols introduced there. The proposed design can be used with various methods for operating the modular braking adjuster 1. Herein, one possibility is active current and voltage modulation with the modular braking adjuster 1. The submodules 2 can be viewed collectively as a controllable voltage source. In simplified terms, the modular braking adjuster 1 modulates a voltage u.sub.BR across the series circuit of the submodules 2 and thus generates a current i.sub.BR by the modular braking adjuster 1. Herein, this current i.sub.BR has a direct component i.sub.BR,DC and an alternating component i.sub.BR,AC. Herein, the voltage u.sub.BR has a direct component u.sub.BR,DC and an alternating voltage component u.sub.BR,AC, which in each case generate the direct component and alternating component in the current through the braking adjuster. It has been shown that the dynamics and the operating range of the braking adjuster can be increased if the voltage u.sub.BR applied across the submodules assumes negative values. For this purpose, the voltage u.sub.BR is subjected to open-loop or closed-loop control in such a way that the amplitude of the alternating voltage component U.sub.BR,AC is greater than the direct voltage component u.sub.BR,DC. To enable stable operation of the braking adjuster at this operating point, the full-bridge modules are provided in the series circuit. The freely selectable voltage amplitude, even with values above the direct voltage component, enables energy balance of the capacitors of the individual submodules to be ensured. This enables stable operation of the modular braking adjuster with a current through the braking adjuster, wherein this current can assume different polarities. In addition to stable operation, this also ensures high utilization of the operating range of the brake resistor.

(17) The main task of the modular braking adjuster 1 is to convert a defined power into heat over time in the brake resistor 3 or the sum of all braking resistors arranged in series. Herein, the power to be converted into heat is subjected to open-loop or closed-loop control via the direct component i.sub.BR,DC. To ensure energy balance and stability of the modular braking adjuster 1, the current i.sub.BR through the modular braking adjuster has an alternating component i.sub.BR,AC. The amplitude of the alternating component of the current i.sub.BR is designated .sub.AC.

(18) Negative voltages cannot be generated with unipolar submodules, such as, for example, half-bridge modules or double half-bridge modules 22. The realization of the time curve shown in FIG. 7 with values of the voltage u.sub.BR of less than zero therefore requires the use of bipolar submodules, such as, for example, full-bridge modules 21.

(19) Operation at higher power increases the proportion of modulated negative voltages across the series circuit of the submodules 2 thus necessitating the use of further full-bridge modules 21. Likewise, the realization of higher power also leads to a reduction in the modulated negative current through the modular braking adjuster. Since unipolar submodules can only provide a positive terminal voltage, the negative component of the current through the modular braking adjuster is required to maintain energy balance. This limits the use of unipolar submodules. The possible operating range of the modular braking adjuster 1 can be described with the aid of the specific resistance R.sub.spec and the direct component i.sub.BR,DC of the current i.sub.BR through the modular braking adjuster. This operating range is depicted in FIG. 8. The specific resistance R.sub.spec is the resistance value R relative to the DC link voltage U.sub.D, i.e., the operating voltage of the modular braking adjuster 1. For a given system configuration, the direct component i.sub.BR,DC of the current i.sub.BR through the modular braking adjuster 1 is equivalent to the power converted by the modular braking adjuster 1.

(20) Brake actuator variants that are only equipped with unipolar submodules can only be operated in the hatched operating range designated I. Only in this range is the voltage U.sub.BR across the series circuit of the submodules 2 always positive. For example, if the system is equipped with a specific resistance R.sub.spec=0.5 /kV, a maximum direct component i.sub.BR,DC=0.5 I.sub.Nom can be achieved with this design. Herein, I.sub.Nom describes the nominal current of the semiconductor switches used. The proposed modular braking adjuster 1 can likewise be operated in this operating range. If higher powers, i.e., direct components with i.sub.BR,DC>0.5 I.sub.Nom, are to be realized, a negative voltage u.sub.BR must be generated across the series circuit of the submodules 2. This is identified by the operating range II in which operation of the proposed modular braking adjuster 1 is also possible. Compared to the operating range I with only unipolar submodule types, the proposed modular braking adjuster 1 doubles the performance capability of the proposed modular braking adjuster. The operating range III can only be used with a design that only has full-bridge modules 21. Due to the lower voltage that can be generated by a full-bridge module 21 compared to a double half-bridge module 22, the design of a modular braking adjuster 1 with submodules 2 of the full-bridge module 21 type has proven to be uneconomical. In comparison, the proposed modular braking adjuster 1 offers a significantly cheaper and more economical solution.

(21) Overall, fewer submodules are required for the design of the modular braking adjuster. As can be seen from the curves of the voltage to be generated, a higher proportion of positive voltage than negative voltage must be generated. Compared to the full-bridge module 21, twice the positive output voltage can be achieved with the same amount of material with the double half-bridge modules 22. A further decisive advantage of using a combination of double half-bridge modules 22 and full-bridge modules 21 is the possible mechanical design of these two variants. The same components are required to construct the two submodules for a system. Only the busbar connection for the individual modules between the semiconductors and the submodule capacitors is different. However, they offer the same dimensions, cooling water terminals, electric terminals for the busbar, triggers, etc. For such a system, adapting the design, such as, for example, a cabinet system, and the surrounding peripherals to the specific embodiment of the submodules is unnecessary. Rather, the design or cabinet system contains accommodating devices that are able to accommodate full-bridge modules and double half-bridge modules without any changes. The number and ratio of the installed full-bridge modules 21 and double half-bridge modules 22 can thus be freely varied and scaled in a design.

(22) In summary: the invention relates to a modular braking adjuster 1, having a brake resistor 3 and at least two submodules 2, wherein the brake resistor 3 and the submodules 2 are arranged in a series circuit 4. In order to improve the modular braking adjuster 1, it is proposed that at least one submodule 2 is embodied as a full-bridge module 21 and at least one submodule 2 is embodied as a double half-bridge module 22, wherein the modular braking adjuster 1 has a control device, . . . which is configured to generate a voltage u.sub.BR across the submodules 2 arranged in series, wherein the voltage u.sub.BR comprises a direct voltage component u.sub.BR,DC and an alternating voltage component uBRAC, wherein the control device is further configured to provide open-loop control or closed-loop control of the alternating voltage component u.sub.BR,AC, in particular in respect of its amplitude, in such a way that the energy taken up by the modular braking adjuster 1 on average over time is converted into heat in the brake resistor 3, wherein the amplitude of the alternating voltage component u.sub.BR,AC is, at least temporarily, greater than the direct voltage component u.sub.BR,DC. The invention further relates to an electric drive 10 having a modular braking adjuster 1 of this kind and a power converter 5, wherein the power converter 5 is electrically connected on the direct voltage side to the modular braking adjuster 1. The invention further relates to a method for operating a modular braking adjuster 1 of this kind or an electric drive 10 of this kind, wherein the submodules 2 generate a voltage u.sub.BR of this kind across the submodules 2 arranged in series.