Frequency-variable control method for a modular brake actuator

Abstract

The invention relates to a method for operating a modular brake actuator (1), said modular brake actuator (1) comprising at least one sub-module (2) and a brake resistor (3) which are arranged in a series circuit (4). In order to improve the modular brake actuator, a voltage (uBR) is generated by means of the at least one sub-module (2), wherein the generated voltage (uBR) has a direct component ((uBR,aDC) and an alternating component (uBR,aDC); the alternating component (uBR, aDC) is measured such that the electric energy received by the modular brake actuator (1), averaged over time, is converted into heat in the brake resistor (3); and the modulation frequency (fM) of the alternating component (uBR,aDC) is varied on the basis of a sub-load factor (α) of the modular brake actuator (1). The invention also relates to a control device (10) designed to carry out such a method, to such a modular brake actuator (1) comprising such a control device, and to a modular drive unit (20) having a modular multilevel converter (21) and a modular brake actuator (1).

Description

[0001] Description

[0002] Frequency-variable control method for a modular brake controller

[0003] The invention relates to a method for operating a modular brake controller, wherein the modular brake controller comprises at least one submodule and one braking resistor arranged in a series circuit. The invention further relates to a control device and a modular brake controller, wherein the modular brake controller comprises at least one submodule and one braking resistor arranged in a series circuit. The invention further relates to a modular drive unit comprising a modular multi-level power converter and such a modular brake controller, wherein the modular brake controller is electrically connected to a DC voltage side of the modular multi-level power converter.

[0004] A modular multilevel power converter is available from the

[0005] DE 10 103 031 A1 . This power converter, also known as M2C or MMC, has a converter topology which, due to its design with submodules, is particularly suitable for medium and high voltage applications. The basic design of the multi-phase converter comprises two converter arms per phase, each with a series connection of submodules. The two converter arms are connected to one another at the phase connection. The other side of the converter arms is connected to the DC side. The AC side of the modular multilevel power converter is formed by one or more phase connections. In the basic design, the converter can be used to transfer energy bidirectionally between the DC side and the AC side, or to temporarily store it to a certain extent.

[0006] To additionally enable targeted energy dissipation, the installation of a braking controller is advisable. A modular braking controller is known from WO 2007 / 023061 A2. The modular braking controller is typically connected to the DC side of the modular multilevel converter, for example, between a DC+ and a DC- connection.

[0007] The resistance of a brake actuator arrangement is often also referred to as a braking resistor, as it is suitable for converting electrical energy from an electrical machine, which is generated as a result of a braking process, into heat. The use of a braking actuator is not restricted to the application of a braking electric drive. It does not necessarily have to be braking energy that is converted into heat. The braking controller can, for example, also be used to stabilize a power supply network by converting electrical energy from the power supply network into heat. The term braking resistor was chosen in order to distinguish the resistor in which a given electrical energy or power is converted into heat or heat per unit of time from other resistors.

[0008] The term "power to be converted into heat" means that the integral of the power over time is converted into heat. In other words, the amount of energy resulting from the power over time is converted into heat.

[0009] The invention is based on the object of improving a modular brake controller.

[0010] This object is achieved by a method for operating a modular brake controller, wherein the modular brake controller comprises at least one sub-module and a braking resistor which are arranged in a series circuit, wherein a voltage is generated at least temporarily by means of the at least one sub-module, wherein the generated voltage has a direct component and an alternating component, wherein the alternating component is free of direct components and is dimensioned such that the electrical energy absorbed on average over time by the modular brake controller is converted into heat in the braking resistor, wherein a modulation frequency of the alternating component is varied as a function of a partial load factor of the modular brake controller. This object is further achieved by a control device set up to carry out such a method.This object is further achieved by a modular brake controller, wherein the modular brake controller comprises at least one submodule and a braking resistor which are arranged in a series circuit, wherein a voltage can be generated by means of the at least one submodule, wherein the modular brake controller has such a control device for controlling or regulating the at least one submodule. This object is further achieved by a modular drive unit which has a modular multilevel power converter and such a modular brake controller, wherein the modular brake controller is electrically connected to a DC voltage side of the modular multilevel power converter.

[0011] Further advantageous embodiments of the invention are specified in the dependent claims.

[0012] The invention is based, among other things, on the discovery that the modular design of the modular brake controller allows any operating voltage of the brake controller to be implemented. The modular brake controller is typically connected to the intermediate circuit of a power converter in order to convert electrical energy from a drive system or a power supply system into heat. With its modular design, the modular brake controller can be adapted to any desired intermediate circuit voltage by using an appropriate number of submodules.

[0013] The partial load factor a describes the proportion of the active power absorbed by the modular brake resistor in relation to its rated power, at which the maximum current flows through the braking resistor. This is determined by the relationship In other words, the partial load factor indicates what proportion of the maximum power the modular brake controller 1 converts into heat at the current operating point.

[0014] The modulation frequency is the frequency of the alternating component.

[0015] All known types of submodules can be used as submodules. These include, for example, half-bridge modules, double half-bridge modules, or full-bridge modules. The capacitor voltage or the capacitor voltages of the corresponding submodule alone can be used to generate voltages. Alternatively, it is also possible, for example by using pulse width modulation, to generate a voltage through the submodule that is lower than the capacitor voltage or capacitor voltages. Pulse width modulation has proven particularly advantageous for generating different voltages when only one submodule is used.

[0016] In addition, the method for operating the modular braking unit enables the power to be converted into heat to be precisely controlled or regulated. The heat is then obtained from the time integral of the power. The method ensures that not all of the intermediate circuit voltage is dropped across the braking resistor during energy conversion. The advantage lies in the ability to regulate the power to be converted into heat. At the same time, the energy content of the capacitor or capacitors of the at least one submodule or submodules is regulated. This enables stable operation of the modular braking unit even over longer operating periods, in particular for continuous operation. The braking resistor can be arranged at any point in the series circuit. For example, the braking resistor can be arranged between one of the connections of the modular braking unit and a submodule or at any point between two submodules.

[0017] In the event that the modular brake controller is not active, i.e. is not intended to convert electrical energy into heat, the voltage across at least one submodule or the further series connection of submodules is identical to the intermediate circuit voltage, so that no voltage drops across the resistor and therefore no current flows.

[0018] For control or regulation, a voltage is generated across at least one submodule or, if several submodules are arranged in a further series connection, across the further series connection of submodules. A DC component of the voltage is provided for this purpose to control or regulate the power to be converted into heat. To regulate the capacitor voltage or voltages of the submodule(s), an alternating component is superimposed on the DC component.

[0019] Since these voltages cause corresponding currents, it has proven advantageous to limit the rate of change of the voltage. Due to the currents associated with the voltage changes, the modular brake controller is also suitable for brake controllers that have an inductance, for example, as a parasitic inductance of the braking resistor.

[0020] It is particularly advantageous to combine the modular brake controller with the modular multilevel power converter, also known as an M2C power converter, to create a modular drive unit. Identical sub-modules can be used for the modular multilevel power converter and the modular brake controller. The same hardware can also be used to control the sub-modules. Due to the modular design of both the power converter and the modular brake controller, the modular drive unit can be easily adapted to a required power requirement by selecting an appropriate number of sub-modules in the power converter and the modular brake controller. The identical design of the sub-modules in the modular brake controller and the multilevel power converter means that a high proportion of identical parts can be achieved. This has a positive effect on the reliability and manufacturing costs of such a drive unit.

[0021] The modular brake controller can be connected to the DC side of converters of any design and is not limited to use with a modular multilevel converter.

[0022] The DC component of the voltage can be used to generate a current through the modular brake resistor, which also has a further DC component. This DC component flows through the modular brake resistor and therefore also the braking resistor. The current flowing through the braking resistor creates electrical losses. These are used to specifically convert electrical energy into heat. The amount of power to be converted into heat, i.e. energy per unit of time, can be controlled or regulated by the level of the DC component of the voltage, as this directly determines the voltage drop across the resistor and this in turn determines the further DC component of the current through the modular brake resistor.

[0023] The intermediate circuit voltage is applied across the modular brake controller, as it is electrically connected to the intermediate circuit. Thus, the intermediate circuit voltage is applied across the series connection of the brake resistor and the further series connection of the submodules. Instead of the further series connection of submodules, only one submodule can be present. Thus, the modular brake controller, to which the intermediate circuit voltage is applied, absorbs the active power.

[0024] PßR — D ' ßR,DC . The entire active power absorbed by the braking resistor should be converted into heat, since the modular braking resistor should not be designed to absorb and store significant amounts of energy.

[0025] The alternating component is dimensioned in such a way that the electrical energy absorbed over time by the modular brake controller is converted into heat in the braking resistor. The alternating component can be used to influence the capacitor voltages of the sub-modules and to stabilize the modular brake controller. The alternating component of the voltage causes a further alternating component in the current through the modular brake controller by means of a corresponding voltage drop across the braking resistor. Both the alternating component and the further alternating component have a mean value of zero, so that only reactive power is exchanged with the further alternating component of the current and the intermediate circuit voltage or the voltage across the modular brake controller. The alternating component is therefore free of direct component.It has been shown that this portion can be used to exchange energy between the capacitors of the submodules and the resistor. The energy exchange is advantageously controlled or regulated so that the entire active power is converted into heat across the resistor. The electrical energy absorbed by the modular braking resistor, averaged over time, is converted into heat in the braking resistor. The relationship is expressed as an equation. where the current 1 B R through the braking resistor consists of the direct component 1 BR, DC and the alternating component i BRf aDC according to lBR = l BR,DC + l BR,aDC. From this, the alternating component can be determined depending on the voltage waveform that influences the effective value.

[0026] It has been shown that energy oscillations depend on the part-load factor. These are often greatest in the range of a = 0.3. This is energy that is stored in the capacitor of the sub-module and then released again. It has also been shown that the degree of energy oscillation, i.e. the energy fluctuation on the capacitor of the sub-modules, can be reduced by increasing the modulation frequency. It is therefore advantageous to vary or fix the modulation frequency depending on the part-load factor. This allows the capacitance of the capacitors in the sub-modules to be reduced, and both the sub-modules and the modular brake controller to be manufactured more cost-effectively.

[0027] The proposed method provides a variable modulation frequency depending on the operating point. At operating points with higher relative energy ripple or energy oscillation, the modulation frequency fMincreased in order to reduce the voltage fluctuation in the sub-module capacitors. This increases the losses in the semiconductors used. However, since the operating points are in the partial load range, the semiconductors are not at their operating limit at these points and therefore do not need to be designed for higher power levels. Efficiency is also not crucial here, since the operation of the modular braking controller always provides for targeted power conversion or energy dissipation. The operating point-dependent change in the modulation frequency can be implemented in a variety of ways. Both open-loop and active regulation of the modulation frequency is possible.The dependency of the operating point can, for example, be specified via the modulation factor or the part-load factor of the modular braking controller, or it can be recorded using the current through the modular braking controller or the power of the modular braking controller. The modulation frequency can in turn be controlled using specified curves, equations, limit values ​​or lookup tables, to name a few examples. This makes it possible to achieve the desired system behavior, which can influence the utilization between the semiconductors and capacitors used. This makes it possible to reduce the utilization of the capacitors and increase that of the semiconductors in the critical part-load range. In this range, the capacitors have a limiting effect. At operating points with higher braking power, the utilization is in turn shifted from the semiconductors to the capacitors. In these ranges, the semiconductors have a limiting effect.This allows the capacitor energy to be installed to be reduced considerably and the installed hardware of the modular braking unit to be used much more effectively.

[0028] The proposed method provides for operating-point-dependent adjustment of the modulation frequency, which allows the utilization of the various hardware components of the modular braking unit to be shifted depending on the operating point. This allows the capacitor energy to be significantly reduced and, in some cases, even significantly better utilization of the installed hardware of the modular braking unit. The operating-point-dependent control or regulation of the modulation frequency can be achieved in a variety of ways.

[0029] In an advantageous embodiment of the invention, the modular brake controller comprises a plurality of submodules arranged in a further series circuit, wherein the voltage generated by the plurality of submodules is applied across the further series circuit of submodules. By using a plurality of submodules in the further series circuit, the operating voltage of the modular brake controller can be adapted as desired to the intermediate circuit voltage of the power converter. In this case, operating voltages of any desired height, i.e., intermediate circuit voltages in the drive unit, can be realized.

[0030] In a further advantageous embodiment of the invention, the DC component is controlled or regulated as a function of the power to be converted into heat by means of the modular braking controller or as a function of the voltage applied to the modular braking controller. The power to be converted into heat or the voltage applied to the modular braking controller is specified by means of a setpoint. By comparing the setpoint with the actual value, control can be carried out in a simple manner, for example by means of a PI controller. It has therefore proven advantageous to control or regulate the DC component as a function of the power to be converted into heat. This power can in turn depend on other variables, such as the voltage of the capacitor of the submodules of a modular multilevel power converter.If the modular brake controller is operated on a DC link with a DC link capacitor, for example, on a 2-point or 3-point converter, it has proven advantageous to control or regulate the DC component as a function of the DC link voltage. These control structures can be used to implement dynamic controls for converting electrical power into heat, which protects the electric drive unit from overload caused by excessive energy. This energy can result, for example, from the braking process of an electrical machine.

[0031] In a further advantageous embodiment of the invention, the DC component is controlled or regulated in such a way that a current with a further DC component is generated through the modular brake converter, the product of the further DC component and the voltage across the modular brake converter corresponding to a predetermined power to be converted into heat by the modular brake converter, in particular a predetermined active power to be converted into heat by the modular brake converter. The DC component of the voltage is controlled or regulated in such a way that the further DC component of the current is so large that the product of the intermediate circuit voltage and the further DC component corresponds to the value of the power to be converted into heat by the modular brake converter. The power to be converted into heat is energy that is converted into heat in a specific time.Alternatively, it is also possible to define an active power as the power to be converted into heat.

[0032] In a further advantageous embodiment of the invention, the modulation frequency of the alternating component is higher for a partial load factor in the range from 0.2 to 0.4 than for a partial load factor in the range greater than 0.8. It has been shown that the modular brake controller has a high energy oscillation precisely in the range around 0.3 of the partial load factor. At the same time, the flowing currents are low due to the low partial load factor. This allows the modulation frequency to be increased. The higher switching frequency of the semiconductors in the submodules is possible due to the relatively low current. If the partial load factor increases further beyond the value of 0.8, the currents are then so high that the semiconductors switch at a lower frequency and a lower modulation frequency is selected.This has the advantage that the performance of the existing semiconductors is better utilized and thus the capacitance of the capacitors of the submodules can be reduced.

[0033] In a further advantageous embodiment of the invention, the alternating component is used as a manipulated variable for controlling the capacitor voltages of the submodules. In order to compensate for disturbances, it has proven beneficial to use the values ​​of the alternating component determined according to the formulas for feedforward control. The voltage across the capacitors is then controlled by means of a controller. This allows the modular brake controller to operate stably even in the presence of disturbances. Furthermore, operation is independent of changing variables. For example, a change in the resistance value caused by aging or heating can be easily compensated for by the controller.

[0034] In a further advantageous embodiment of the invention, an AC voltage side of the modular multilevel power converter is connected to an energy source, in particular to a power supply network or to an electrical machine. The modular brake controller can be used by connecting it to an energy source to convert excess or unusable energy into heat. The energy source can be, for example, an electrical machine which feeds electrical energy back during a braking process. If this energy can no longer be used, it must be converted into heat by means of the modular brake controller if a mechanical brake is to be dispensed with. In contrast to a mechanical brake, the electrical energy is converted into heat without wear, so that the use of the modular brake controller is more economical in operation.

[0035] It is also possible to use the modular multilevel power converter for energy transmission. In this case, it may be advisable to provide a modular brake controller in the event that the transmitted energy cannot be taken off. This ensures that this type of energy transmission remains in operation even if the reception of energy is disrupted. The energy transmission system can remain in operation during this disruption, reliably avoiding the need for costly restarts and shutdowns, which can also lead to stability problems in the energy supply network. The modular brake controller therefore also increases the reliability and availability of a modular drive unit designed for energy transmission.

[0036] In a further advantageous embodiment of the invention, the control device of the modular drive unit is designed to determine the power to be converted into heat as a function of the voltage of the capacitor of the submodules of the modular multilevel power converter. In a modular multilevel power converter, energy stored in the power converter is not necessarily reflected in the intermediate circuit voltage as is the case, for example, with a 2-point or 3-point power converter. In the modular multilevel power converter, an increased energy content affects the stored energy, i.e. the voltage, of the capacitor or capacitors in the respective submodules of the modular multilevel power converter.In order to specifically reduce the energy content in the modular multilevel power converter, it has proven advantageous to determine the power to be converted into heat for the control or regulation of the DC component as a function of the voltage of the capacitor of the respective submodules of the modular multilevel power converter. A possible method for operating an electric drive unit with a modular power converter and a proposed modular brake controller regulates or controls the DC component of the voltage across the further series connection of the submodules of the modular brake controller as a function of the voltage of the capacitor or capacitors of the submodules of the modular multilevel power converter.

[0037] The invention will be described and explained in more detail below with reference to the exemplary embodiments shown in the figures. They show:

[0038] FIG 1 a modular brake controller,

[0039] FIG 2 to FIG 4 Examples of the submodule, FIG 5 Time profiles of voltage and current, FIG 6 Effects of the control method on the

[0040] Energy swings and

[0041] FIG 7 to FIG 9 are examples of the modular drive unit.

[0042] FIG. 1 shows a modular brake controller 1. This has a series circuit 4 of at least one submodule 2 and a braking resistor 3. The series circuit 4 can have a plurality of submodules 2. These, in turn, are arranged as part of the series circuit 4 in a further series circuit 41. The modular brake controller 1 is designed to be connected at its terminals 11 to an intermediate circuit 9 of a power converter.

[0043] Across the further series circuit 41 of the submodules 2, a voltage U B R . With the generated voltage U BR can be a current i BR by the modular brake controller 1. The current i BR also flows through the braking resistor 3 and causes the conversion of electrical energy into heat. The operating voltage U is across the modular braking resistor 1. D If the modular brake controller 1 is connected to the intermediate circuit of a power converter, the intermediate circuit voltage is applied to the modular brake controller. In this case, the modular brake controller 1 is said to be connected to the DC side of the power converter.

[0044] Figures 2 to 4 show exemplary embodiments of submodules 2. All known submodules 2, in particular the submodules 2 of Figures 2 to 4, are suitable for implementing the proposed method. To avoid repetition, reference is made to the description of Figure 1 and the reference symbols introduced therein.

[0045] The illustrated embodiments of the submodules 2 comprise at least two semiconductor switches and at least one capacitor. By switching operations of the semiconductor switches, an output voltage U SU b are generated at the terminals of the submodule 2. A control device 10 transmits the control signals to the semiconductor switches of the submodule 2. The control device 10 is preferably arranged outside the submodule 2 and is therefore not part of the submodule 2. Rather, it has proven advantageous to control all submodules 2 of the modular brake actuator 1 with one control device 10. In addition, the control device 10 can carry out the calculations required for the control and regulation of the voltages and currents. Thus, the control device 10 can determine the required current 1 from the specified value of the power to be converted into heat. B R through the modular brake controller 1. To determine this current iB R, a voltage determined, controlled, or regulated by the control device 10 is generated across the submodules 2 of the further series circuit 41 by means of corresponding control signals. In the following exemplary embodiments, the control device 10 is not shown for reasons of clarity.

[0046] FIG 2 shows a so-called half-bridge module. This has two semiconductor switches and a capacitor. The voltage U is applied to the capacitor. c , S ub . By switching operations of the semiconductor switches, the output voltage U SU b of zero or U c , S ub are generated at the terminals of submodule 2 .

[0047] FIG 3 shows a so-called double bridge module. This has four semiconductor switches and two capacitors. The voltage U is applied to each capacitor. Ci , S U b or U C2 , sub an . By switching operations of the semiconductor switches, the output voltage U SU b of zero , one of the capacitor voltages U Ci , sub , U C 2 , sub or the sum of the capacitor voltages Uci , sub , U C 2 , sub are generated at the terminals of submodule 2 .

[0048] FIG 4 shows a so-called full-bridge module. This has four semiconductor switches and a capacitor. The voltage U is applied to the capacitor. c , S ub . By switching actions of the semiconductor switches, the output voltage U SU b of zero, the positive or the negative capacitor voltage ± U c , sub are generated at the terminals of submodule 2 .

[0049] FIG 5 shows a selection of possible time profiles for the voltage U generated across the further series circuit B R and the current flowing through the modular brake controller 1 BR . The alternating part u BR , aD c can be sinusoidal. Alternatively, the alternating component u BR , aD c can also be obtained from the superposition of two sine functions with different frequencies. As a further alternative, the voltage waveform and the current waveform of the alternating component u B R, aB c be block-shaped or trapezoidal. All of these designs can be used to control or regulate the modular brake actuator.

[0050] FIG. 6 shows the normalized energy fluctuation AE as a function of the partial load factor a. At 0% and 100%, i.e. at idle and full load, the energy fluctuation AE is at its lowest. Then, the largest part of the conversion into heat is already caused by the DC component. However, in the range of a = 0.3, the energy fluctuation AE is at its greatest. Since this value also affects the modulation frequency f MThe absolute value of the energy oscillation AE can be reduced by increasing the modulation frequency. This is particularly possible in the range around a = 0.3, since the semiconductor's conduction losses are still low there and the semiconductor can realize additional losses by increasing the switching frequency.

[0051] The energy ripple increases significantly in the partial load range. In other power electronic circuits, the energy ripple typically increases with the output power.

[0052] The energy oscillation AE is a measure of the energy that must be stored in the capacitor of submodule 2. It thus determines the capacitor's capacitance. By reducing the energy oscillation, the capacitors in the submodules can be designed with lower capacitance values. This makes the submodule and the entire modular braking controller more cost-effective.

[0053] FIG 7 shows a modular drive unit 20 with a modular multilevel power converter 21 and a modular brake controller 1. These are connected to one another via the intermediate circuit 9, to which the voltage UD is applied. The modular multilevel power converter 21 can, but not necessarily, have the same submodules 2 as the modular brake controller 1. The series connection of the submodules 2 of the modular multilevel power converter 21 also has an inductance 8, which improves the control behavior of the modular multilevel power converter 21. The connections LI, L2, L3 represent the AC voltage side connections or, in short, the AC voltage side of the modular multilevel power converter 21. In this exemplary embodiment, the modular multilevel power converter 21 is of three-phase design.Alternatively, a single-phase version with neutral conductor or any desired number of phases is possible by providing a corresponding number of phase modules in the modular multilevel power converter 21.

[0054] FIG. 8 shows an exemplary embodiment of a modular drive unit 20. A power source 5 is electrically connected to the AC voltage side of the modular multilevel power converter 21. The power source can be, for example, a power grid 6 or an electrical machine 7.

[0055] In the exemplary embodiment in FIG 9, the modular drive unit 20 has two modular multilevel power converters 21 and a modular brake converter 1, which are electrically connected to one another at the intermediate circuit 9. A first of the two modular multilevel power converters 21 is connected on its AC voltage side to a power supply network 6 and a second of the two modular multilevel power converters 21 is connected on its AC voltage side to an electrical machine 7. The electrical machine 7 can be supplied with electrical energy from the power supply network 6. Feeding energy back from the electrical machine 7 into the power supply network 6, for example during a braking process, is also possible with the modular drive unit 20.If the power supply network 6 is not capable of absorbing the energy, the electrical energy generated by the electric machine 7 can be advantageously converted into heat by means of the modular brake controller 1. A mechanical brake subject to wear can be dispensed with in this embodiment.

Claims

Patent claims 1. Method for operating a modular brake controller (1), wherein the modular brake controller (1) has at least one submodule (2) and a braking resistor (3), which are arranged in a series circuit (4), wherein at least temporarily by means of the at least one submodule (2) a voltage (U B R), whereby the generated voltage (U B R) a constant component (u BR , D c) and an alternating portion (u BR , aD c), whereby the alternating portion (u BR , aD c) is free of DC components and is dimensioned such that the electrical energy absorbed on average by the modular brake resistor (1) is converted into heat in the brake resistor (3), wherein a modulation frequency (f M ) of the alternating portion (u BR , aDc) is varied depending on a partial load factor (a) of the modular brake actuator (1).

2. Method according to claim 1, wherein by means of the DC component (U BR ,DC) the power to be converted into heat is controlled or regulated, whereby by means of the alternating component (u BR , aD c) t corresponding to the constant component (u BR , D c) is superimposed, the capacitor voltage or the capacitor voltages of the submodule (2) or the submodules (2) is or are regulated.

3. Method according to one of claims 1 or 2, wherein the modular brake controller (1) comprises a plurality of sub-modules (2) arranged in a further series circuit (41), wherein by means of the plurality of sub-modules (2) the generated voltage (U B R) is applied across the further series connection (41) of the submodules (2).

4. Method according to one of claims 1 to 3, wherein the DC component (u BR , Dc) depending on the power to be converted into heat by means of the modular brake controller (1) or depending on the voltage (U D ) is controlled or regulated.

5. The method according to claim 4, wherein the DC component (U B R, DC ) is controlled or regulated in such a way as to produce a current (i BR ) with a further DC component (i BRfDC ) by the modular brake controller (1), whereby the product of the further DC component (i BRfDC ) and the voltage (U D ) above the modular brake controller (1) corresponds to a predetermined power to be converted into heat by the modular brake controller (1), in particular a predetermined active power to be converted into heat by the modular brake controller (1).

6. Method according to one of claims 4 or 5, wherein the modulation frequency (f M ) of the alternating portion (u BR,aoc) is greater for a partial load factor (a) in the range of 0.2 to 0.4 than for a partial load factor (a) in the range greater than 0.

8.

7. The method according to any one of claims 1 to 6, wherein the alternating portion (u B R,aoc) as a control variable for the capacitor voltages (U c , SU b) the submodules (2) are used.

8. Control device (10) configured to carry out a method according to one of claims 1 to 7.

9. Modular brake controller (1), wherein the modular brake controller (1) comprises at least one sub-module (2) and a braking resistor (3) which are arranged in a series circuit (4), wherein by means of the at least one sub-module (1) a voltage (u BR ), wherein for controlling or regulating the at least one submodule (2) the modular brake controller (1) has a control device (10) according to claim 8.

10. Modular brake controller (1) according to claim 9, wherein the modular brake controller (1) comprises a plurality of sub-modules (2) arranged in a further series circuit (41), wherein by means of the plurality of sub-modules (2) a created tension (U B R) across the further series circuit (41).

11. Modular drive unit (20) comprising a modular multilevel power converter (21) and a modular brake controller (1) according to one of claims 9 or 10, wherein the modular brake controller (1) is electrically connected to a DC voltage side of the modular multilevel power converter (21).

12. Modular drive unit (20) according to claim 11, wherein an AC voltage side of the modular multilevel power converter (21) is connected to an energy source (5), in particular to an energy supply network (6) or to an electrical machine (7).

13. Modular drive unit (20) according to one of claims 11 or 12, wherein the control device (10) is configured to determine the power to be converted into heat as a function of the voltage of the capacitor of the submodules of the modular multilevel power converter (21).

Images