Asymmetrical 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). In order to improve the modular brake actuator, a square-wave or trapezoidal voltage (uBR) is generated by means of the sub-module (2), wherein the square-wave or trapezoidal voltage (uBR) has a direct component (uBR,DC) and an alternating component (uBR,aDC); the alternating component (uBR,aDC) is formed by an upper voltage value (uBR,AC1), which is present for a first period of time (τ1), and a lower voltage value (uBR,AC2), which is present for a second period of time (τ2); the output which is to be converted into heat is controlled or regulated using the direct component (uBR,DC); and the capacitor voltage or the capacitor voltages of the sub-module (2) or the sub-modules (2) is / are regulated using the alternating component (uBR,aDC) which is superimposed with the direct component (uBR,DC). The invention also relates to a control device (10) designed to carry out such a method, to a modular brake actuator (1) comprising such a control device, and to a modular drive unit (20) having a modular multilevel converter (21) and such a modular brake actuator (1).

Description

[0001]Description Asymmetric control method for a modular braking controller The invention relates to a method for operating a modular braking controller, wherein the modular braking 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 braking controller, wherein the modular braking 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 multilevel power converter and such a modular braking controller, wherein the modular braking controller is electrically connected to a DC voltage side of the modular multilevel power converter. A modular multilevel power converter is known from DE 10103 031 A1.This power converter, also known as M2C or MMC, has a converter topology that, thanks to its submodule design, 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 each other 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 its basic design, the converter can be used to bidirectionally transfer energy between the DC and AC sides or to temporarily store it to a certain extent. To additionally enable targeted energy dissipation, the installation of a braking unit is advisable.A modular braking unit is known from WO 2007 / 023061 A2. The modular braking unit is typically connected to the DC voltage side of the modular multilevel power converter, for example, between a DC+ and a DC- connection. The resistance of a braking unit 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 unit is not limited to the application of a braking electric drive. Thus, it does not necessarily have to be braking energy that is converted into heat. The braking unit can also be used, for example, to stabilize a power grid by converting electrical energy from the power grid 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 time from other resistors. The term “power to be converted into heat” means in the following that the integral of the power over time is converted into heat. In other words, an amount of energy resulting from the power over time is converted into heat. The invention is based on the object of improving a modular braking actuator. This object is achieved by a method for operating a modular braking actuator, wherein the modular braking actuator comprises at least one submodule and a braking resistor which are arranged in a series circuit, wherein at least temporarily a block-shaped or trapezoidal voltage is generated by means of the at least one submodule, wherein the block-shaped or trapezoidal voltageA trapezoidal voltage has a DC component and an alternating component, the alternating component being free of DC components and dimensioned such that the electrical energy absorbed by the modular brake actuator over time is converted into heat in the braking resistor. The alternating component is formed by an upper voltage value, which is present for a first period of time, and a lower voltage value, which is present for a second period of time, the first period of time and the second period of time being unequal. Furthermore, this object is achieved by a control device configured to carry out such a method.This object is further achieved by a modular braking controller, wherein the modular braking controller comprises at least one submodule and a braking resistor arranged in a series circuit, wherein a block-shaped or trapezoidal voltage can be generated by means of the at least one submodule, wherein the modular braking 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 comprising a modular multilevel power converter and such a modular braking controller, wherein the modular braking controller is electrically connected to a DC voltage side of the modular multilevel power converter. Further advantageous embodiments of the invention are specified in the dependent claims.The invention is based, among other things, on the finding that the modular design of the modular braking actuator allows any operating voltage to be implemented. Typically, the modular braking actuator is 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 braking actuator can be adapted to any desired intermediate circuit voltage by using an appropriate number of submodules. 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 alone or the capacitor voltages of the corresponding submodule 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(s). Pulse width modulation has proven particularly advantageous for generating different voltages when only one submodule is used. 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 derived from the time integral of the power. The method ensures that not the entire intermediate circuit voltage drops across the braking resistor during energy conversion. The advantage lies in being able to regulate the power to be converted into heat. At the same time, the energy content of the capacitor(s) of the at least one submodule(s) is regulated.This enables stable operation of the modular braking unit even over longer operating periods, particularly for continuous operation. The braking resistor can be arranged anywhere in the series circuit. For example, the braking resistor can be arranged between one of the terminals of the modular braking unit and a submodule, or anywhere between two submodules. In the event that the modular braking unit is not active, i.e. is not intended to convert electrical energy into heat, the voltage applied across at least one submodule or the further series connection of submodules is identical to the intermediate circuit voltage, so that no voltage drop across the resistor and therefore no current flows.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. For the control or regulation of the power to be converted into heat, a DC component of the voltage is provided for this purpose. To regulate the capacitor voltage or the capacitor voltages of the submodule(s), an alternating component is superimposed on the DC component. The superposition of the DC component and the alternating component results in a block-shaped voltage curve. The block-shaped curve, in turn, requires that the voltages across the further series connection can be changed as quickly as desired. This leads to an infinite voltage gradient. Since these voltages cause corresponding currents, it has proven advantageous to limit the rate of change of the voltage change.Due to the currents associated with the voltage changes, the modular braking unit is also suitable for braking units that have inductance, for example as parasitic inductance of the braking resistor. The block-shaped voltage then becomes a trapezoidal voltage. The block-shaped or trapezoidal curve of the alternating component is formed by an upper voltage value, which is present for a first time period, and a lower voltage value, which is present for a second time period, whereby the first time period and second time period are unequal. This makes the block-shaped curve asymmetrical and the corresponding process can also be described as asymmetrical. To ensure that the alternating component is free of DC voltage, the products of the upper or lower voltage value and the first or second time period are equal in amount. The upper voltage value is a positive value and the lower voltage value a negative value.With a block-shaped curve, the sum of the first and second time periods is, in the simplest case, identical to the period of the recurring control. With a trapezoidal signal, the time for the rising and falling edges is also added. However, since these time periods are short compared to the first and second time periods, they can be neglected in the energy analysis. It has proven advantageous that with the block-shaped or trapezoidal voltage, high energy can be exchanged at comparatively low amplitudes of the voltage across the further series connection of the submodules and of the current flowing through the modular braking unit, since the energy results from the time integral of the current or from the integral of the square of the current. This means that high performance can be achieved.This high performance refers to the power to be converted into heat as well as to the cable used to stabilize the sub-modules. In other words, due to the relatively low amounts of current and voltage, in particular low amplitudes or low maximum values ​​in the current and voltage curves, comparatively high rms values ​​can be achieved, which are crucial for conversion into heat by the braking resistor. Due to the low amplitude and low fluctuation range through the use of the block or trapezoidal shape of the voltage and the associated currents, the semiconductor switches of the sub-modules can be designed for a lower current load. Alternatively, it is possible to use the modular braking controller to convert higher power into heat. The block-shaped orA trapezoidal voltage can be easily generated by a control device that controls the semiconductor switches of the submodule or the submodules of the further series connection. The block-shaped or trapezoidal voltage is then applied across the submodule or across the further series connection of submodules. It is particularly advantageous to combine the modular braking unit with the modular multilevel converter, also known as an M2C converter, to form a modular drive unit. Identical submodules can be used for both the modular multilevel converter and the modular braking unit. Likewise, the same hardware can be used to control the submodules.Due to the modular design of both the power converter and the modular braking unit, the modular drive unit can be easily adapted to the required power requirement by selecting an appropriate number of sub-modules in the power converter and the modular braking unit. Due to the identical design of the sub-modules in the modular braking unit and the multi-level power converter, 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. The modular braking unit can be connected to the DC voltage side of power converters of any design and is not limited to use with a modular multi-level power converter. The block-shaped or trapezoidal voltage generated by the sub-modules has a DC component and an alternating component. To achieve the block-shaped orIn addition to the trapezoidal curve, the alternating component also has a block-shaped or trapezoidal curve. The DC component of the voltage can be used to generate a current through the modular braking unit, which also has a further DC component. This DC component flows through the modular braking unit and thus 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, in turn, the further DC component of the current through the modular braking unit. The intermediate circuit voltage is applied across the modular braking unit, as it is electrically connected to the intermediate circuit.The intermediate circuit voltage is therefore applied across the series connection of the braking resistor and the further series connection of the submodules. Instead of the further series connection of submodules, only one submodule can be present. The modular braking unit, to which the intermediate circuit voltage is applied, thus absorbs the active power ^^^ோ ൌ ^^^ ∙ ^^^ோ,^^ (1). The entire active power absorbed by the braking resistor should be converted into heat, since the modular braking unit should not be designed to absorb and store significant amounts of energy. The alternating component has a block-shaped or trapezoidal curve, which is dimensioned such that the electrical energy absorbed by the modular braking unit on average over time is converted into heat in the braking resistor. The alternating component can be used to influence the capacitor voltages of the submodules and to stabilize the modular braking unit.The alternating component of the voltage causes a further alternating component in the current through the modular braking unit 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 braking unit. The alternating component is therefore free of direct component. It has been shown to be advantageously used to exchange energy between the capacitors of the submodules and the resistor. The energy exchange is advantageously controlled or regulated in such a way that the entire active power across the resistor is converted into heat.The electrical energy absorbed by the modular brake actuator over time is converted into heat in the braking resistor. The relationship is expressed as an equation. where the current i BR by the braking resistor from the DC component i BR,DC and the alternating share i BR,aDCaccording to ^^^ோ ൌ ^^^ோ,^^ ^ ^^^ோ,^^^ (3). From this, the alternating component can be determined depending on the voltage waveform that influences the effective value. The deviation of the alternating component from a symmetrical curve can improve the energy exchange within the modular braking unit. This means that the capacitors in the sub-modules can be dimensioned smaller. For example, the maximum chopper voltage can be limited to a predefined limit as the sum of the upper voltage value and the DC component. This limit is greater than the intermediate circuit voltage. Subject to the above equations and the boundary condition that the effective current value of the modular braking unit remains the same, the values ​​for the upper and lower voltage values ​​as well as the first and second time periods are obtained.This results in different current and voltage waveforms, which can also be referred to as half-waves, even if the durations differ. In other words, the maximum chopper voltage is the sum of the upper voltage value and the DC component. For the first period, the maximum chopper voltage is limited to a threshold value. Due to the unchanged effective value, the power converted in the modular braking unit corresponds to the value resulting from the product of the DC component and the intermediate circuit voltage. Limiting the voltage results in significantly higher currents in the second period, which promote the conversion of electrical energy into heat.In an advantageous embodiment of the invention, the modular braking unit comprises a plurality of submodules arranged in a further series circuit, wherein the block-shaped or trapezoidal voltage is generated across the further series circuit of the submodules by means of the plurality of submodules. By using a plurality of submodules in the further series circuit, the operating voltage of the modular braking unit can be adapted as required to the intermediate circuit voltage of the power converter. In this case, operating voltages of any desired level, i.e. intermediate circuit voltages in the drive unit, can be realized. 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 unit or as a function of the voltage applied to the modular braking unit.The power to be converted into heat or the voltage applied to the modular braking unit is specified using a setpoint. By comparing the setpoint with the actual value, control can be carried out easily, for example using 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 in the submodules of a modular multilevel converter. If the modular braking unit is operated on an intermediate circuit with an intermediate circuit 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 intermediate circuit voltage.These control structures can be used to implement dynamic controls for converting electrical power into heat, which protect the electric drive unit from overloading due to excessive amounts of energy. These amounts of energy can result, for example, from the braking process of an electrical machine. 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 braking unit, wherein the product of the further DC component and the voltage across the modular braking unit corresponds to a predetermined power to be converted into heat by the modular braking unit, in particular a predetermined active power to be converted into heat by the modular braking unit.The voltage level of 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 that can be converted into heat by the modular braking unit. The power to be converted into heat is energy that is converted into heat in a specific time. Alternatively, it is possible to specify an active power as the power to be converted into heat. In a further advantageous embodiment of the invention, the sum of the upper voltage value and the DC component is limited to a limit value that is independent of operation. This reduces the maximum voltage that can be generated by the submodules. This makes it possible to reduce the number of submodules. This enables a cost-effective design of the modular braking unit.Since the energy fluctuations in the modular braking unit are reduced at the same time, the submodules can also be implemented with capacitors of lower capacitance. This also contributes to cost-effective expansion. In a further advantageous embodiment of the invention, the alternating component is used as a manipulated variable for regulating 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 regulated by means of a control system. This allows the modular braking unit 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 control system.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 grid or to an electrical machine. By connecting it to an energy source, the modular braking unit can be used to convert excess or unusable energy into heat. The energy source can, for example, be an electrical machine that feeds electrical energy back during a braking process. If this energy can no longer be used, it must be converted into heat using the modular braking unit if a mechanical brake is to be dispensed with. In contrast to a mechanical brake, the conversion of electrical energy into heat occurs without wear, so that the use of the modular braking unit is more economical in operation.It is also possible to use the modular multilevel power converter for power transmission. In this case, it may be advisable to provide a modular braking unit in the event that the transmitted power cannot be taken off. This ensures that such a power transmission remains operational even if the power reception is disrupted. The power transmission system can remain in operation during this disruption, reliably avoiding the need for time-consuming shutdown and restart, which could also lead to stability problems in the power supply network. Thus, the modular braking unit also increases the reliability and availability of a modular drive unit designed for power transmission.In a further advantageous embodiment of the invention, the control device of the modular drive unit is configured to determine the power to be converted into heat as a function of the capacitor voltage 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(s) 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 controlling or regulating the DC component as a function of the voltage of the capacitor of the respective submodules of the modular multilevel power converter. One possible method for operating an electric drive unit with a modular power converter and a proposed modular braking controller regulates or controls the DC component of the voltage across the further series connection of the submodules of the modular braking controller as a function of the voltage of the capacitor or capacitors of the submodules of the modular multilevel power converter. The invention is described and explained in more detail below with reference to the exemplary embodiments illustrated in the figures.9 to 11 exemplary embodiments of the modular drive unit. FIG. 1 shows a modular braking unit 1. This has a series connection 4 of at least one submodule 2 and a braking resistor 3. The series connection 4 can have a plurality of submodules 2. These are in turn arranged as part of the series connection 4 in a further series connection 41. The modular braking unit 1 is designed to be connected at its connections 11 to an intermediate circuit 9 of a power converter. A voltage u can be generated across the further series connection 41 of the submodules using a control device 10. BR generate. With the voltage u BR a current can beBR by the modular braking unit 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 applied across the modular braking controller 1. DIf the modular braking unit 1 is connected to the intermediate circuit of a power converter, the intermediate circuit voltage is applied to the modular braking unit. In this case, the modular braking unit 1 is said to be connected to the DC voltage side of the power converter. Figures 2 to 4 show exemplary embodiments of submodules 2. All known submodules, in particular the submodules of Figures 2 to 4, are suitable for implementing the proposed method. To avoid repetition, reference is made to the description of FIG. 1 and the reference numerals introduced there. The illustrated exemplary 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 subare generated at the terminals of submodule 2. A control device 10 transmits the control signals to the semiconductor switches of submodule 2. The control device 10 is preferably arranged outside of submodule 2 and is therefore not part of the submodule. Rather, it has proven advantageous to control all submodules 2 of the modular braking unit 1 with one control device 10. In addition, the control device 10 can perform the calculations required for the control and regulation of the voltages and currents. Thus, the control device 10 can determine the required current through the modular braking unit i from the specified value of the power to be converted into heat. BR To determine this current i BRTo generate a voltage across the submodules of the further series circuit 41, a voltage determined, controlled, or regulated by the control device 10 is generated by appropriate control signals. In the following exemplary embodiments, the control device 10 is not shown for reasons of clarity. Figure 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,sub By switching actions of the semiconductor switches, the output voltage U sub of zero or U C,sub at the terminals of submodule 2. Figure 3 shows a so-called double-bridge module. This has four semiconductor switches and two capacitors. The voltage U is applied to each capacitor. C1,sub or U C2,sub By switching operations of the semiconductor switches, the output voltage U subof zero, one of the capacitor voltages U C1,sub , U C2,sub or the sum of the capacitor voltages U C1,sub , U C2,sub generated at the terminals of submodule 2. Figure 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,sub By switching actions of the semiconductor switches, the output voltage U sub of zero, the positive or the negative capacitor voltage ±U C,sub generated at the terminals of submodule 2. FIG 5 shows the time course of the voltage u BR across the submodules 2 of the further series circuit 41 for the proposed method. To avoid repetition, reference is made to the description of Figures 1 to 4 and the reference symbols introduced there. The voltage u BR consists of a constant component and BR,DC and an alternating portion uBR,aDC together. The voltage u BR for a first time τ1the maximum chopper voltage u BR,max because the DC component U BR,DC with the upper voltage value u BR,AC1 To achieve the required effective value of the current through the braking resistor i BR,eff To generate the first time period τ1 is greater than half the period T. Due to the second time period τ2 being smaller than the first time period τ1, the lower voltage value u BR,AC2 greater than the upper voltage value u BR,AC1, so that the alternating component is free of DC components. Due to the finite voltage gradient shown, the voltage curve shown is trapezoidal. The idealized curve with infinite voltage gradient, which results in a block-shaped time curve, is also shown in dashed lines. A trapezoidal or block-shaped curve is also referred to when the individual trapezoids or blocks do not have the same shape, but are different. However, the blocks or trapezoids of the alternating component have the same area. The effects of the generated voltage u BR on the current through i BRthrough the braking resistor is shown in FIG. 6. The relatively low voltage in the first time range τ1 leads to a small current in this time range. To achieve the required effective value, the current in the second time range τ2 is therefore significantly higher. If the first time period τ1 and the second time period τ2 are chosen to be equal to form the alternating component, a symmetrical time characteristic is created. Depending on the partial load factor α, the values ​​shown for maximum chopper voltage u result. BR,maxand energy oscillations ΔE, which are shown in FIG. 7 in standardized form. The energy oscillations cause an energy fluctuation on the capacitor of submodule 2. The energy oscillation ΔE is a measure of the energy that must be stored in the capacitor of submodule 2. It therefore determines the dimensioning of the capacitor in terms of its capacity. The partial load factor α indicates what proportion of the maximum power the modular braking unit 1 converts into heat at the current operating point. The advantages of the proposed method are shown in FIG. 8, where the first time period τ1 and the second time period τ2 differ. By limiting the maximum chopper voltage u BR,max, in this case to the value 1.05 of the intermediate circuit voltage, the voltage to be generated by submodules 1 is reduced. Therefore, fewer submodules are required for operation, making the modular braking unit simpler and more cost-effective to implement. Furthermore, the asymmetrical curve also has the advantage that the energy oscillations ΔE are significantly reduced, so that the capacitors of the submodules can be dimensioned with lower capacitance. This simplifies the design of the submodules and makes the modular braking unit more cost-effective and therefore more economical. It can be seen that with the proposed method for the modulation type explained as an example, the number of submodules to be installed can be reduced by ~20% and the capacitor energy to be installed by ~65%. The method can also be applied analogously to other modulation types of the modular braking unit.The proposed method can also be used to reduce the limit of the maximum chopper current by increasing the maximum modulated chopper voltage. FIG. 9 shows a modular drive unit 20 with a modular multilevel power converter 21 and a modular braking unit 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 braking unit 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 terminals L1, L2, L3 represent the AC voltage side terminals, 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 designed as a three-phase unit. Alternatively, a single-phase version with a 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. FIG. 10 shows an exemplary embodiment of a modular drive unit 20. An energy source 5 is electrically connected to the AC voltage side of the modular multilevel power converter 21. The energy source can be, for example, a power supply network 6 or an electrical machine 7. In the exemplary embodiment in FIG. 11, the modular drive unit 20 has two modular multilevel power converters 21 and a modular braking unit 1, which are electrically connected to one another at the intermediate circuit 9.In this case, a first of the two modular multilevel power converters 21 is connected on its AC side to a power supply network 6 and a second of the two modular multilevel power converters 21 is connected on its AC side to an electrical machine 7. The electrical machine 7 can be supplied with electrical energy from the power supply network 6. The modular drive unit 20 also makes it possible to feed energy back from the electrical machine 7 to the power supply network 6, for example during a braking process. If the power supply network 6 is not capable of absorbing the energy, the electrical energy generated by the electrical 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

Claims 1. Method for operating a modular brake actuator (1), wherein the modular brake actuator (1) comprises at least one sub-module (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 sub-module (2) a block-shaped or trapezoidal voltage (u BR ), whereby the block-shaped or trapezoidal voltage (u BR ) a DC component (u BR,DC ) and an alternating portion (u BR,aDC ), whereby the alternating portion (u BR,aDC ) by an upper voltage value (u BR,AC1 ), which is present for a first time period (τ1), and a lower voltage value (u BR,AC2 ), which is present for a second time period (τ2), wherein the first time period (τ1) and second time period (τ2) are unequal, 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,aDC ), which corresponds to the equal part (u BR,DC ) is superimposed, the capacitor voltage or the capacitor voltages of the submodule (2) or the submodules (2) is or are regulated.

2. Method according to claim 1, wherein the modular brake actuator (1) comprises a plurality of submodules (2) which are arranged in a further series circuit (41), wherein by means of the plurality of submodules (2) the block-shaped or trapezoidal voltage (u BR ) is generated across the further series circuit (41) of the submodules (2).

3. Method according to one of claims 1 or 2, wherein the DC component (u BR,DC ) depending on the power to be converted into heat by means of the modular brake actuator (1) or depending on the voltage (U D) is controlled or regulated.

4. Method according to claim 3, wherein the DC component (u BR,DC ) is controlled or regulated in such a way as to produce a current (i BR ) with another equal component (i BR,DC ) by the modular brake actuator (1), whereby the product of the further DC component (i BR,DC ) and the voltage (U D ) across the modular brake actuator (1) corresponds to a predetermined power to be converted into heat by the modular brake actuator (1), in particular a predetermined active power to be converted into heat by the modular brake actuator (1).

5. Method according to one of claims 3 or 4, wherein the sum of the upper voltage value (u BR,AC1 ) and DC component (u BR,DC ), to an operation-independent limit value (u BR,max ) is limited.

6. The method according to any one of claims 1 to 5, wherein the alternating portion (u BR,aDC) as a control variable for the capacitor voltages (U C,sub ) of the submodules (2).

7. Control device (10) configured to carry out a method according to one of claims 1 to 6.

8. Modular brake actuator (1), wherein the modular brake actuator (1) comprises at least one submodule (2) and a braking resistor (3) arranged in a series circuit (4), wherein by means of the at least one submodule (1) a block-shaped or trapezoidal voltage (u BR ), wherein for controlling or regulating the at least one submodule (2), the modular brake actuator (1) has a control device (10) according to claim 7.

9. Modular brake actuator (1) according to claim 8, wherein the modular brake actuator (1) comprises a plurality of submodules (2) which are arranged in a further series circuit (41), wherein by means of the plurality of submodules (2) a block-shaped or trapezoidal voltage (u BR) can be generated via the further series circuit (41).

10. Modular drive unit (20) comprising a modular multilevel power converter (21) and a modular braking controller (1) according to one of claims 8 or 9, wherein the modular braking controller (1) is electrically connected to a DC voltage side of the modular multilevel power converter (21). u 11. Modular drive unit (20) according to claim 10, 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).

12. Modular drive unit (20) according to one of claims 10 or 11, 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).

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