Method for operating an electric power converter, computer program product, control device for an electric power converter, power converter, and electric drive

Abstract

The invention relates to a method (100) for operating an electric power converter (2), wherein the power converter (2) has two connections, namely an input (4) for an input voltage and an output (5) for an output voltage, and is designed to convert the input voltage into the output voltage, the method (100) having a step (S10) of initializing an overload value and the following steps (S20-S50) which are carried out repeatedly: - obtaining current information which describes the present current strength value of an electric current flowing at one of the connections; - determining a weighting value by evaluating a weighting function, which assigns a weighting value to at least one current strength variable, using the current strength value as the current strength variable, the weighting function assigning a first weighting value to current strength variable values at a specified current strength threshold and assigning a weighting value higher than the first weighting value to current strength variable values above the specified current strength threshold; - determining an incremental value on the basis of the present current strength value, the weighting value, and a continuous current value in such a way that the current strength has a positive effect on the magnitude of the incremental value and the continuous current value has a negative effect on the magnitude of the incremental value; and - determining an updated overload value by cumulatively linking the previous overload value and the incremental value.

Description

[0001] Method for operating an electrical power converter, computer program product, control device for an electrical power converter, power converter and electrical drive

[0002] The present invention relates to a method for operating an electrical power converter. The invention also relates to a computer program, a control device for an electrical power converter, a power converter, and an electric drive.

[0003] To prevent overloading of power converters and / or the devices they supply, it is known to determine an overload value for which the positive deviation of the square of a current flowing at an input or output of the power converter from the square of a predetermined continuous permissible current is integrated over time. For this purpose, an incremental value is determined, and then—starting from an initial overload value—an updated overload value is calculated by cumulatively combining the previous overload value with the incremental value. This technique is also known as I 2 t-Derating is known and is based on the finding that electrical power loss is essentially proportional to the square of the RMS current.

[0004] From DE 10 2023 105 114 A1, for example, a method is known in which a current flowing through an electronic safety element is detected, an I 2The t-offset value is determined by multiplying a predefined evaluation interval by the square of a predefined offset current, and an I 2 The t-value is determined by multiplying the evaluation interval by the square of the detected current. A tripping time for the fuse element is determined based on an I 2 The residual value of t is determined, which corresponds to a difference of I 2 t-value and I 2 corresponds to the t-offset value. Such a conventional I 2 However, t-Derating does not meet the needs of all applications, especially for complex power converters in electric drives for vehicles.

[0005] The invention is therefore based on the objective of providing an improved method for determining an overload value, particularly with regard to automotive applications.

[0006] This problem is solved according to the invention by a method for operating an electrical power converter, wherein the power converter has two terminals, namely an input for an input voltage and an output for an output voltage, and is configured to convert the input voltage into the output voltage, wherein the method comprises a step of initializing an overload value and the following repeatedly executed steps: obtaining current information which describes an instantaneous current value of an electric current flowing at one of the terminals;Determining a weighting value by evaluating a weighting function that assigns a weighting value to at least one current variable, using the current value as the current variable, wherein the weighting function assigns a first weighting value to values ​​of the current variable at a given current threshold and assigns a higher weighting value than the first weighting value to values ​​of the current variable above the given current threshold; determining an incremental value as a function of the instantaneous current value, the weighting value, and a continuous current value, such that the current has a positive influence on the magnitude of the incremental value and the continuous current value has a negative influence on the magnitude of the incremental value; and determining an updated overload value by cumulatively combining the previous overload value and the incremental value.

[0007] The power converter used in the inventive method has two terminals. These terminals are an input and an output. The power converter is configured to convert the input voltage into the output voltage.

[0008] The method according to the invention comprises a step of initializing an overload value. The method according to the invention further comprises the following steps. These are repeated:

[0009] The process includes a step of obtaining current information. This current information describes the instantaneous value of an electric current. The electric current flows at one of the terminals.

[0010] The procedure further includes a step of determining a weighting value by evaluating a weighting function using the current value as the current variable. The weighting function assigns a weighting value to a current variable. The weighting function assigns an initial weighting value to values ​​of the current variable at a given current threshold. The weighting function assigns a higher weighting value than the initial weighting value to values ​​of the current variable above the given current threshold.

[0011] The procedure further includes a step of determining an incremental value as a function of the instantaneous current value, the weighting value, and a constant current value. This determination is carried out such that the current value has a positive influence on the magnitude of the incremental value, and the constant current value has a negative influence on the magnitude of the incremental value.

[0012] The method further comprises a step of determining an updated overload value by cumulatively combining the previous overload value and the incremental value. The invention is based on the understanding that exceeding the permanently permissible current has a greater impact on the actual overload the higher the current, so that conventional I 2 t-derating approaches do not realistically represent the actual overload. Is a limit value for the overload value used in such conventional I 2If, for example, t-deratings are designed based on a maximum permissible current, this limit is reached relatively early by slight exceedances of the continuously permissible current, even though the converter or a device supplied by it is not actually overloaded yet. The method according to the invention therefore proposes to include weighting functions in the determination of the incremental value, which allows for a corresponding weighting of the current value. In this way, relatively minor exceedances of the continuously permissible current have a lesser impact on the incremental value and thus on the overload value.

[0013] Advantageously, this avoids an unrealistic increase in the overload value. This unlocks further performance reserves of the power converter or the device it supplies. For example, an electrically powered vehicle can thus be operated at high load for extended periods without the user being subjected to a forced reduction in torque and / or power.

[0014] According to a preferred embodiment, an RMS value of the instantaneous current is used as the instantaneous current value.

[0015] In detail, the weighting function can be monotonically increasing above the current threshold. The weighting function can have a maximum value for the current variable, up to which the weighting function is defined. The weighting function can be linear between the current threshold and the maximum value. It is also possible for the weighting function to have several disjoint intervals between the current threshold and the maximum value, in which the weighting function exhibits different behavior. Typically, the weighting function increases more sharply in higher intervals than in lower intervals.

[0016] According to a particularly easy-to-implement first embodiment, the weighting function assigns values ​​of the current variable below the current threshold either the value assigned to the current threshold or a lower value. If a lower value is assigned, it should preferably be only slightly below the value assigned to the current threshold so as not to mask a healing effect below the current threshold. This healing effect is based on the assumption that the power converter or the device supplied by it regenerates itself from previous overloads.

[0017] According to a second embodiment, the weighting function assigns a second weighting value to current variable values ​​at a second current threshold that is not higher than the first current threshold, and assigns a higher weighting value to current variable values ​​below the second current threshold. This allows for an accelerated recovery effect, as described previously, for values ​​below the second current threshold. This means that below the second current threshold, such a significant drop in the permissible current can be assumed that the power converter or the device it supplies recovers from previous overloads. This unlocks further performance reserves.

[0018] In a further development of the second design variant, it can be provided that a current threshold interval exists between the first and second current thresholds, within which the value of the current variable is assigned the first weighting value, the second weighting value, or a weighting value lying between the first and second weighting values. This current threshold interval can prevent unavoidable measurement noise or errors from affecting the overload value, particularly when current values ​​are very close to the continuously permissible current.

[0019] Preferably, to determine the incremental value, a product of the weighting value and a difference between a current value dependent on a square of the instantaneous current value and the continuous current value is calculated.

[0020] According to a preferred embodiment, the method according to the invention further comprises the following step: obtaining speed information that describes an instantaneous rotational speed or a feed frequency of an electric machine supplied by the converter. The rotational speed can be provided by a speed sensing device associated with the electric machine. In synchronous machines, the fundamental feed frequency is directly proportional to the rotational speed of the machine, so the fundamental feed frequency is used as the feed frequency. In asynchronous machines, the fundamental feed frequency deviates from its proportionality to the rotational speed by the slip frequency in operating conditions in which a non-zero torque is generated. That is, the fundamental feed frequency minus the slip frequency is proportional to the rotational speed of the machine.

[0021] The slip frequency is positive when the machine generates motor torque at positive speeds, and negative when it generates generator torque at positive speeds. Similarly, the slip frequency is negative when the machine generates motor torque at negative speeds, and positive when it generates generator torque at negative speeds.

[0022] Therefore, in asynchronous machines, a fundamental frequency feed rate corrected for the slip frequency is preferably used as the feed frequency. In this respect, the term "speed" is used in the following as a generic term for both rotational speed and feed frequency.

[0023] The weighting function can assign a weight value to each pair of current and velocity variables. Furthermore, the weighting function can assign higher weight values ​​to velocity variables below a predefined velocity threshold than to values ​​above that threshold.

[0024] Preferably, the following step of the method can also be provided: Determining a velocity weighting value by evaluating a velocity weighting function that assigns a velocity weighting value to a velocity variable, using the rotational velocity as the velocity variable, wherein the velocity weighting function assigns a first velocity weighting value to values ​​of the velocity variable at a predetermined velocity threshold and assigns a higher velocity weighting value than the first velocity weighting value to values ​​of the velocity variable below the predetermined velocity threshold. The current value can be a product of the velocity weighting value and the square of the instantaneous current value.

[0025] In a further advantageous embodiment, the velocity weighting function assigns a second weight value to values ​​of the velocity variable at a given second velocity threshold that lies below the first velocity threshold. The velocity weighting function can assign values ​​of the velocity variable below the second velocity threshold either the value assigned to the second velocity weighting value or a higher value. Alternatively or additionally, the velocity weighting function can be monotonically decreasing from the second velocity threshold to the first velocity threshold.

[0026] The square of the current value can be used as the current strength value.

[0027] According to a particularly easy-to-implement variant of the method according to the invention, when determining the incremental value, a predetermined value is used as the continuous current value, which describes a square of a predetermined permanently permissible current strength of the electric current flowing at the connection.

[0028] With the additional advantage, the method can alternatively include the following step: Determining the continuous current value using a continuous current value function which assigns the continuous current value to the velocity variable, using the rotational velocity as the velocity variable, wherein the continuous current value function assigns a first continuous current value to values ​​of the velocity variable at a given velocity threshold and assigns a lower continuous current value than the first continuous current value to values ​​of the velocity variable below the given velocity threshold, wherein the continuous current value function is monotonically increasing, in particular quadratically increasing, above the velocity threshold.

[0029] The continuous current function can assign a second continuous current value to values ​​of the velocity variable at a given second velocity threshold that lies below the first velocity threshold. In particular, it is possible that the continuous current function is monotonically increasing, especially quadratically increasing, below the second velocity threshold, and monotonically increasing, especially cubically increasing, from the second velocity threshold to the first velocity threshold.

[0030] In a preferred embodiment of the method according to the invention, the weighting function assigns the weighting value depending on a flow rate information, which describes a flow rate of a coolant, and / or a temperature information, which describes a coolant temperature. This allows the 2t-Derating can be further improved by taking into account the current cooling efficiency.

[0031] The function in question can be evaluated by retrieving values ​​from a look-up table or by analytically calculating the function.

[0032] The inventive method can further provide that, in the initialization step, an overload value dependent on the converter's idle time is initialized. For idle times above a threshold, a predetermined starting value of the overload value is initialized, while for idle times below the threshold, an overload value, particularly one dependent on the idle time and greater than the starting value, is determined and initialized. This allows for the consideration of healing effects that occur during temporary idle operation. The starting value is typically zero.

[0033] The method according to the invention can further provide that the power converter has semiconductor switching elements for converting the input voltage into the output voltage, wherein the method further comprises the following steps: determining a throttling value from the overload value; controlling the semiconductor switching elements as a function of the throttling value; wherein, when controlling the semiconductor switching elements, the current at the output or at the input is limited if the updated overload value exceeds a predetermined overload threshold. The power converter can be designed as an inverter and configured to convert a DC voltage as the input voltage into a single-phase or multi-phase AC voltage as the output voltage. Preferably, the current information describes the output voltage as the magnitude of a space vector describing the multi-phase AC voltage.Alternatively, the current information can describe the current in one phase of the multi-phase alternating voltage or the current of the single-phase alternating voltage.

[0034] The power converter can alternatively be designed as a DC-DC converter and configured to convert a DC voltage as input voltage into a DC voltage as output voltage.

[0035] The electrical machine connected to the converter can be a drive motor for a vehicle. The converter's output can be connected to a stator winding or a slip ring of an electrically excited synchronous machine, or to an inductive transformer for the excitation winding of an electrically excited synchronous machine. Alternatively, the converter is used as part of an oil pump, an air conditioning compressor, a clutch actuator, or a parking lock actuator. The converter can also be located at the output of a high-frequency transformer in an inductive transmission system.

[0036] The problem underlying the invention is further solved by a computer program product comprising instructions which, when the program is executed by a computer, cause it to perform the steps of the method described above.

[0037] The problem underlying the invention is further solved by a control device for an electrical power converter, which power converter has two terminals, namely an input for an input voltage and an output for an output voltage, and is configured to convert the input voltage into the output voltage, wherein the control device has an initialization section, which is configured to initialize an overload value, and a calculation section; wherein the calculation section is configured to repeatedly obtain current information, which describes an instantaneous current value of an electric current flowing at one of the terminals, and to determine a weighting value by evaluating a weighting function, which assigns a weighting value to at least one current variable, using the current value as the current variable.wherein the weighting function assigns a first weight value to values ​​of the current variable at a given current threshold and assigns a higher weight value to values ​​of the current variable above the given current threshold than the first weight value, to determine an incremental value as a function of the instantaneous current value, the weight value and a continuous current value, such that the current has a positive effect on the magnitude of the incremental value and the continuous current value has a negative effect on the magnitude of the incremental value, and to determine an updated overload value by cumulatively combining the previous overload value and the incremental value.

[0038] The problem underlying the invention is further solved by a power converter comprising a previously described control device and semiconductor switching elements for converting the input voltage into the output voltage.

[0039] The power converter can include a current measuring device for acquiring current information. Alternatively, the electric drive includes a measuring input for receiving current information, for example from a higher-level vehicle control unit.

[0040] If the current information describes the instantaneous current value at the output of the converter, a further control device may be provided in which the current information describes the instantaneous current value at the input of the converter.

[0041] The problem underlying the invention is further solved by an electric drive for a vehicle, comprising an electric machine and a previously described power converter, which is designed as an inverter and configured to provide the electric machine with a multiphase alternating voltage as an output voltage. Alternatively or additionally, the electric drive according to the invention comprises a previously described power converter, which is designed as a DC-DC converter and configured to provide the excitation windings of a rotor of the electric machine with a DC voltage as an output voltage.Alternatively or additionally, the electric drive according to the invention has a previously described power converter, which is designed as an inverter and is configured to provide an alternating voltage as output voltage to a primary side of an inductive high-frequency transformer for excitation windings of a rotor of the electric machine (3).

[0042] All descriptions of the inventive method can be applied analogously to the inventive computer program product, the inventive control device, the inventive power converter, and the inventive electric drive, so that the aforementioned advantages can also be achieved with these. In particular, the calculation section can be configured to perform the repeated steps of the method. Further sections of the control device can also be provided that are configured to perform the steps of the method.

[0043] Further advantages and details of the present invention will become apparent from the exemplary embodiments described below and from the drawings. These are schematic representations and show: Fig. 1 a block diagram of an exemplary embodiment of the electric drive according to the invention;

[0044] Fig. 2 shows a flowchart of a first embodiment of the method according to the invention;

[0045] Fig. 3 is a signal flow diagram to illustrate the first embodiment of the method according to the invention;

[0046] Fig. 4 shows a signal flow diagram to illustrate a second embodiment of the method according to the invention;

[0047] Fig. 5 shows a flowchart of a third embodiment of the method according to the invention;

[0048] Fig. 6 is a signal flow diagram to illustrate the third embodiment of the method according to the invention;

[0049] Fig. 7 shows a flowchart of a fourth embodiment of the method according to the invention;

[0050] Fig. 8 is a signal flow diagram to illustrate the fourth embodiment of the method according to the invention;

[0051] Fig. 9 shows a flowchart of a fifth embodiment of the method according to the invention;

[0052] Fig. 10 is a signal flow diagram to illustrate the fifth embodiment of the method according to the invention; and

[0053] Fig. 11 is a schematic diagram of a vehicle. Fig. 1 is a block diagram of an exemplary embodiment of an electric drive 1.

[0054] The electric drive 1 comprises an embodiment of a power converter 2 and an electric machine 3. The power converter 2 has two terminals, namely an input 4 for an input voltage and an output 5 for an output voltage, and is configured to convert the input voltage into the output voltage.

[0055] In the present embodiment, the power converter 2 is configured as an inverter and is designed to convert a DC voltage as the input voltage into a three-phase AC voltage as the output voltage. The electric machine 3 is an asynchronous motor or a permanent magnet or electrically excited synchronous motor, whose stator windings can be supplied by the power converter 2 to generate a rotating magnetic field. For the sake of simplicity, additional power electronics for the excitation winding of the electrically excited synchronous motor are not shown.

[0056] The power converter 2 has a power section 6 comprising several semiconductor switching elements 7, which are shown as IGBTs for illustrative purposes. According to the present embodiment, in which the power converter 2 is configured as an inverter, these are connected in pairs to form half-bridges. A center tap of each half-bridge is connected to the output 5.

[0057] Also shown is an intermediate circuit capacitor 8 of the power converter 2.

[0058] The power converter 2 further comprises a control unit 9. The control unit 9 has a control section 10, which is configured to control the semiconductor switching elements 7 (in a generally known manner) for converting the input voltage into the output voltage, for example, by means of pulse-width modulated control signals. Also shown are an initialization section 11 and a calculation section 12 of the control unit 9. It should be noted that sections 10 to 12 of the control unit 9 represent a functional subdivision of the control unit 9, which does not necessarily correspond to the implementation by one or more hardware components.

[0059] The function of the control device 9 is discussed below using several exemplary embodiments of a method 100 for operating the power converter 2.

[0060] Fig. 2 is a flowchart of a first embodiment of method 100. Fig. 3 is a signal flowchart to illustrate the first embodiment of method 100. Blocks 14 to 20 and 22 to 25 shown in the signal flowchart illustrate data processing operations, which are implemented in particular by corresponding instructions of a computer program of the computation section 12.

[0061] The procedure includes a step S10 of initializing an overload value Eo, for the execution of which the initialization section 11 (see Fig. 1) is provided.

[0062] The overload value E₀ is initialized depending on the converter's idle time. If the idle time exceeds a threshold value, a predefined starting value, e.g., zero, of the overload value Eo is initialized. The threshold value is chosen to correspond to a time period after which the overload effects caused by the converter's power loss can be assumed to have completely dissipated. This process is also referred to as healing. For idle times below the threshold value, an overload value Eo, which is greater than the starting value and depends on the idle time, is determined and initialized. This simulates partial healing, which occurs, for example, when a vehicle equipped with the drive unit 1 is briefly out of service, e.g., for the duration of a recovery break.The procedure includes a further step S20 of obtaining current information, for the execution of which the calculation section 12 (see Fig. 1) is specifically designed. The current information describes the RMS value of an instantaneous current I_act of an electric current flowing at output 5 as the magnitude of a space vector. To provide the current information, the power converter 2 has a current measuring device 13 (see Fig. 1).

[0063] The procedure includes a further step S30 of determining a weighting value g(I_act).

[0064] The determination is carried out by evaluating a weighting function g(i), which assigns a weight value g to at least one current variable i. The current variable i is the instantaneous current value Iact. As best illustrated in Fig. 3 by block 14, the weighting function g(i) assigns a first weight value, which here is exemplary one, to values ​​of the current variable i at a given current threshold Ith, and a higher weight value than the first weight value to values ​​of the current variable above the given current threshold Ith.

[0065] In the present embodiment, the first weighting function g(i) is monotonically increasing above the current threshold Ith. More precisely, it is defined piecewise linearly and progressively increasing above the current threshold. For values ​​of the current variable below the current threshold Ith, the weighting function g(i) assigns the weighting value g(Ith) associated with the current threshold Ith, which here is, for example, one.

[0066] The first weighting function g(i) is evaluated either by retrieving function values ​​from a lookup table or by analytically calculating the first weighting function g(i). Analytical calculation can be implemented by defining the weighting function g(i) using polynomials or piecewise-defined polynomials.

[0067] The procedure includes a further step S40 of determining an incremental value AE, for the execution of which calculation section 12 (see Fig. 1) is specifically designed. The incremental value AE is thus determined as a function of the instantaneous current value lact, the weighting value g(I_act), and a continuous current value Icont. 2 determined that the current intensity is positive in the magnitude of the incremental value AE and the continuous current value Icont 2 negatively impacts the amount of the incremental value AE. As a continuous current value, Icont 2 A predefined value is used, which describes the square of a predefined continuous permissible current Icont of the electric current flowing at output 5. In the present embodiment, the current threshold Ith is slightly above the continuous permissible current Icont in order to reduce the influence of unavoidable measurement errors and signal noise on the incremental value AE.

[0068] In detail, the incremental value AE is calculated as the product (see multiplier block 15) of the weighting value g(I_act) and a difference (see summing block 16) between the square (see multiplier block 17) of the instantaneous current value lact and the continuous current value Icont. 2 calculated.

[0069] The procedure includes a further step S50 of determining an updated overload value Eact, for which calculation section 12 (see Fig. 1) is specifically designed. This determination is carried out by cumulatively combining (see integrator block 18) the previous overload value Et-1 and the incremental value ΔE. Specifically, the cumulative combination is performed by calculating the sum of the previous overload value Et-1 and the incremental value ΔE. Simultaneously, the updated overload value Eact is determined such that it is not less than zero (see limit symbol 19). Qualitatively, the updated overload value E(t) thus forms the integral

[0070] P t

[0071] E(t) = ∫₀ᵗ g(Iact(τ))·(Iact²(τ) - Icont²)dτ

[0072]

[0073] Yes

[0074] and thus a weighted I²t value.

[0075] The procedure includes a further step S60 of determining a throttling value from the overload value Eact, for which calculation section 12 (see Fig. 1) is specifically designed. For this purpose, a function f(x) is evaluated, which assigns a throttling value f to a value x. The updated overload value Eact is used as the value. As illustrated by block 20 in Fig. 3, the throttling value drops below one when the overload threshold Eth is exceeded. Analogous to step S30, the function can be evaluated using a lookup table or analytically.

[0076] The procedure includes a further step S70 of controlling the semiconductor switching elements 7 depending on the throttling value f(Eact) wherein when controlling the semiconductor switching elements 7 the current at output 5 is limited if the updated overload value Eact exceeds the overload threshold Eth.

[0077] Steps S20 to S70 are repeated continuously.

[0078] Further embodiments of method 100 are explained below. Only the differences from the first embodiment or from any other preceding embodiment are listed. Identical or equivalent components are identified by identical reference numerals.

[0079] Fig. 4 is a signal flow diagram illustrating a second embodiment of method 100, which, apart from the differences described below, corresponds to the first embodiment. According to the second embodiment, in step S30, the weighting function g(i) assigns a second weighting value g(lth,2) to values ​​of the current variable i when a second current threshold Ith, 2 is not above the first current threshold Ith, and assigns a higher weighting value g(lth,2>) to values ​​of the current variable i below the second current threshold Ith, 2. Between the first current threshold Ith and the second current threshold Ith, 2 lies a current threshold interval Ith-Ith, 2, in which the first weighting value g(lth) is assigned to the value of the current variable.Alternatively, the second weighting value g(lth,2) or a weighting value between the first and second weighting values ​​can be assigned. The current threshold interval Ith-Ith, 2 also serves to reduce the influence of measurement errors and signal noise.

[0080] Fig. 5 is a flowchart of a third embodiment of method 100. Fig. 6 is a signal flowchart illustrating the third embodiment of method 100, the representation of which corresponds to that in Fig. 3. The third embodiment corresponds to the first or second embodiment except for the differences described below.

[0081] Method 100 according to the third embodiment comprises a step S25 for obtaining speed information, for the execution of which, in particular, the calculation section 12 (see Fig. 1) is provided. The speed information describes an instantaneous rotational speed ωact of the electric machine 3 supplied by the converter 2. To provide the speed information, the drive 1 has a speed detection device 21 (see Fig. 1), e.g., a resolver, since the electric machine 3 exhibits asymmetrical phase loads when powered with direct current or quasi-direct current. With regard to step S30, according to the third embodiment, the weighting function g(i,ω) assigns the weighting value g to each pair of the current variable i and a speed variable w.The weighting function g(i,ω) assigns higher weighting values ​​g(lact, Wact) to values ​​of the velocity variable below a given velocity threshold wth (not shown in Fig. 5 for clarity) than to values ​​above the given velocity threshold.

[0082] By taking the rotational speed ωact into account, high currents at very low speeds, which occur, for example, when slowly overcoming inclines or obstacles such as curbs with high torque, are given greater consideration. This is because in such situations, a disproportionate load occurs on the electric machine 3 and the drive converter 2.

[0083] Qualitatively, the updated overload value E(t) thus forms the integral

[0084] P t

[0085] ^(0 I 9 (J act(.1'') > ^00) ' (4zctC0 Icont)dT

[0086]

[0087] Yes

[0088] and thus a weighted I 2 t-value.

[0089] Fig. 7 is a flowchart of a fourth embodiment of method 100. Fig. 8 is a signal flowchart to illustrate the fourth embodiment of method 100. The fourth embodiment corresponds to the first or second embodiment except for the differences described below, but also includes step S25 of the third embodiment.

[0090] The method 100 according to the fourth embodiment comprises a step S26 of determining a velocity weighting value, for the execution of which in particular the calculation section 12 (see Fig. 1) is provided.

[0091] The velocity weighting value is determined by evaluating a velocity weighting function h(w), which assigns a velocity weighting value h to a velocity variable w, using the rotational velocity ω. act as velocity variables. Block 23 in Fig. 8 shows the curve of the velocity weighting function h(w). The velocity weighting function assigns values ​​of the velocity variable w at a given velocity threshold ω. th,1 a first velocity weighting value h(ω) th,1 ) to and values ​​of the velocity variable w below the specified velocity threshold ω th,1 a higher velocity weighting value than the first velocity weighting value h(ω) th,1 ) to.

[0092] Values ​​of the velocity variable w at a given second velocity threshold wth,2, which is below the first velocity threshold ω th,1 For values ​​of the velocity variable that lie below the second velocity threshold, the velocity weighting function h(w) has a second weighting value h(wth,2). For values ​​of the velocity variable that lie below the second velocity threshold, the velocity weighting function h(w) has the second velocity weighting value h(ω). th,2 ) or, according to an alternative version not shown, a higher value. Between the second ω th,2 speed threshold and the first speed threshold ω th,1The velocity weighting function h(w) is monotonically decreasing. Analogous to step S30, the function can be evaluated using a lookup table or analytically. According to the fourth embodiment, in step S30, the current value is a product (see multiplier block 22) of the velocity weighting value h(ω). act ) and the square of the instantaneous current value lact 2 used. That is, to determine the incremental value AE, the incremental value AE is calculated as the product (see multiplier block 15) of the weighting value g(I_act) and a difference (see summing block 16) between the current value h(cüact)-lact. 2 and the continuous current value Icom 2 calculated.

[0093] In this way, the previously mentioned stronger influence of the current at low rotational speeds w on the overload value can be represented. Qualitatively, the updated overload value E(t) thus forms the integral.

[0094] rt

[0095] I ' lactfj'') ^cont)^

[0096]

[0097] Yes

[0098] away.

[0099] Fig. 9 is a flowchart of a fifth embodiment of method 100. Fig. 10 is a signal flowchart to illustrate the fifth embodiment of method 100. The fourth embodiment corresponds to the first or second embodiment except for the differences described below, but also includes step S25 of the third embodiment.

[0100] Method 100 according to the fifth embodiment includes a step S27 for determining the continuous current value, for the execution of which calculation section 12 (see Fig. 1) is specifically provided. The determination is carried out using a continuous current value function lcont. 2 (w), which of the velocity variables w determines the continuous current value Icont 2assigns, using the rotational speed ω act as velocity variables. The continuous current value function lcont 2 (w) assigns a first continuous current value lcont to values ​​of the velocity variable w at a given velocity threshold oath.3 2 (wth,3) and values ​​of the velocity variable w below the specified velocity threshold ω th,3 a lower continuous current value than the first continuous current value I cont 2 (ω th,3 ) to. Given a second velocity threshold wth,4, which is below the first velocity threshold ω th,3 lies, the continuous current value function I cont 2 (ω) a second continuous current value I cont 2 (ω th,4 ) to.

[0101] In Fig. 10, the continuous current value function k(w) is represented by a block 24 and a squaring block 25. Block 24 illustrates the velocity-dependent behavior of the continuously permissible current or the square root of the continuous current value function lcont(w). This makes it clear that the continuous current value function I cont 2 (ω) above the first velocity threshold ω th,3 The velocity increases quadratically. Below the second velocity threshold ω th,4 the continuous current value function I cont 2 (ω) also increases quadratically. From the second velocity threshold ω th,4 to the first speed threshold ω th,3 the continuous current value function I cont 2 (ω) increasing more strongly than quadratically, here exemplarily cubically increasing.

[0102] This means that in step S30, instead of the specified continuous current value I cont 2which is determined by evaluating the continuous current value function I cont 2 (ω) determined continuous current value I cont 2 (ω act ) is used as the continuous current value. In this way, the previously mentioned stronger influence of the current at low rotational speeds w on the overload value can be represented.

[0103] In particular, this applies in the case of a value of the velocity variable that is smaller in absolute value than ω. th,4 The continuous standstill current is output as a continuous current from block 24. In the case of a value of the velocity variable that is greater in magnitude than ω th,3 The continuous current for the rotating machine 3 is output as the current continuous current from block 24. To achieve a smooth transition between the continuous standstill current and the continuous current for the rotating machine, a linear crossfade is applied in the interval between ω. th,4 and ω th,3This was done. In this way, the previously mentioned stronger influence of the current at low rotational speeds w on the overload value can be represented. Qualitatively, the updated overload value E(t) thus forms the integral.

[0104] rt

[0105] E(t) = ∫₀ᵗ g(I act (τ)) · (I² act (τ) − I² cont (ω act ))dτ

[0106]

[0107] Yes

[0108] away.

[0109] In the embodiments using speed information, an alternative to directly detecting the rotational speed can be the use of speed information that describes the supply frequency of the electric machine 3. For synchronous motors, the fundamental frequency supply frequency can be used directly. For asynchronous motors, a fundamental frequency supply frequency corrected for a slip frequency is used as the supply frequency.

[0110] In all previously described embodiments, it is additionally possible for the weighting function to assign the weighting value depending on a flow rate information, which describes a flow rate of a coolant, and / or a temperature information, which describes a coolant temperature.

[0111] In all the previously described embodiments, it is also possible to calculate the RMS value from a peak current value. In this case, a further step (not shown) of determining the RMS value of the instantaneous current can be performed by multiplying the peak value by a factor of the rotational speed ω. act dependent conversion factor, which above a first threshold of the rotational speed 2 -1 / 2The rotational speed should be one below a second threshold and monotonically decreasing from the second threshold to the first threshold.

[0112] Referring again to Fig. 1, an (additional) control unit 9' of the converter 2 can be provided as an alternative or in addition to the control unit 9. In step S20, this control unit 9' receives current information that describes the instantaneous current value lact of an electric current flowing at input 4, here a direct current. To provide the current information, the converter 2 has a current measuring device 13' on its input side, which is shown here as an example arranged between input 4 and the intermediate circuit capacitor 8 in a positive DC line. Alternatively, the current measuring device 13' can also be arranged between the intermediate circuit capacitor 8 and the power section 6 and / or in a negative DC line. Alternatively, the current information at input 4 of the converter 2 can be provided by using model-based algorithms that determine this current from other sensor information.Furthermore, the explanations regarding the control device 9 and the embodiments of the method 100 can be transferred to this control device.

[0113] Instead of the current measuring device 13 shown in Fig. 1, a current measuring device 13" can be provided in all the aforementioned embodiments, which is integrated into the commutation cells forming the semiconductor switching element 7. The current measuring device 13" comprises a current sensor for each phase, which is connected between a negative DC voltage line and the center tap.

[0114] If the electrical machine 3 is an electrically excited synchronous motor, an electrical converter (not shown), designed as a DC-DC converter, can be provided as an alternative or additional measure to the electrical converter 2. The control device 9 of this converter receives current information describing a direct current supplied at the output of the DC-DC converter for supplying slip rings of the electrically excited synchronous motor. In this case, the current measuring device can be arranged at the output of the DC-DC converter. Alternatively, the electrical converter 2 can be designed as an inductive transmission system configured to transmit an excitation current to the rotor of the electrically excited synchronous motor. In this case, the control device 9 of the electrical converter can receive current information describing the current of an alternating current, typically single-phase, supplied at the input of the inductive transmission system.

[0115] Fig. 11 is a schematic diagram of a vehicle 200 which has an electric drive 1 according to one of the previously described embodiments for driving the vehicle 200.

[0116] Alternatively or additionally, a power converter 2 can be designed as part of an oil pump, a high-voltage air conditioning compressor, a clutch actuator or a parking lock actuator of the vehicle 200 according to one of the previously described embodiments.

Claims

Patent claims 1. Method (100) for operating an electrical power converter (2), wherein the power converter (2) has two terminals, namely an input (4) for an input voltage and an output (5) for an output voltage, and is configured to convert the input voltage into the output voltage, wherein the method (100) comprises a step (S10) of initializing an overload value and the following repeatedly executed steps (S20-S50): - Receiving current information that describes the instantaneous current value of an electric current flowing at one of the terminals; - Determining a weighting value by evaluating a weighting function that assigns a weighting value to at least one current variable, using the current value as the current variable, wherein the weighting function assigns a first weighting value to values ​​of the current variable at a given current threshold and assigns a higher weighting value than the first weighting value to values ​​of the current variable above the given current threshold; - Determining an incremental value as a function of the instantaneous current value, the weighting value, and a constant current value, such that the current has a positive influence on the magnitude of the incremental value and the constant current value has a negative influence on the magnitude of the incremental value; and - Determining an updated overload value by cumulatively linking the previous overload value and the incremental value.

2. The method of claim 1, wherein An RMS value of the instantaneous current is used as the instantaneous current value.

3. Method according to claim 1 or 2, wherein the weighting function is monotonically increasing above the current threshold.

4. Method according to any one of the preceding claims, wherein The weighting function assigns the weighting value associated with the current threshold or a lower value to values ​​of the current variable that lie below the current threshold.

5. Method according to any one of claims 1 to 3, wherein The weighting function assigns a second weight value to values ​​of the current variable at a second current threshold that is not above the first current threshold, and assigns a higher weight value to values ​​of the current variable below the second current threshold than to the second weight value, wherein there is a current threshold interval between the first current threshold and the second current threshold, in which the value of the current variable is assigned the first weight value or the second weight value or a weight value between the first weight value and the second weight value.

6. Method according to any one of the preceding claims, wherein To determine the incremental value, a product is calculated from the weighting value and a difference between a current value dependent on the square of the instantaneous current value and the continuous current value.

7. Method according to any of the preceding claims, further comprising the following step (S25): - Receiving speed information that describes an instantaneous rotational speed or a feed frequency of an electrical machine (3) supplied by the power converter (2).

8. Method according to claim 7, wherein The weighting function assigns a weight value to each pair of current variable and velocity variable, whereby the weighting function assigns higher weight values ​​to values ​​of the velocity variable below a given velocity threshold than to values ​​above the given velocity threshold.

9. Method according to claim 7 or 8, if dependent on claim 6, further comprising the following step (S26): - Determining a velocity weighting value by evaluating a velocity weighting function which assigns a velocity weighting value to a velocity variable, using the rotational velocity as the velocity variable, wherein the velocity weighting function assigns a first velocity weighting value to values ​​of the velocity variable at a given velocity threshold and assigns a higher velocity weighting value than the first velocity weighting value to values ​​of the velocity variable below the given velocity threshold; where the current value is a product of the velocity weighting value and the square of the instantaneous current value, The velocity weighting function assigns a second weighting value to values ​​of the velocity variable at a given second velocity threshold that lies below the first velocity threshold, where the velocity weighting function - assigns the value assigned to the second speed weighting value or a higher value to values ​​of the speed variable below the second speed threshold and / or - the speed threshold from the second speed threshold to the first speed threshold decreases monotonically.

10. Method according to any one of claims 6 to 8, wherein The square of the current value is used as the current value.

11. Method according to any one of claims 8 to 10, further showing the following step (S27): - Determining the continuous current value using a continuous current value function which assigns the continuous current value to the velocity variable, using the rotational velocity as the velocity variable, wherein the continuous current value function assigns a first continuous current value to values ​​of the velocity variable at a given velocity threshold and assigns a lower continuous current value than the first continuous current value to values ​​of the velocity variable below the given velocity threshold, wherein the continuous current value function is monotonically increasing, in particular quadratically increasing, above the velocity threshold; Where the continuous current value function assigns a second continuous current value to values ​​of the velocity variable at a given second velocity threshold that lies below the first velocity threshold, wherein the continuous current value function - below the second velocity threshold, the velocity increases monotonically, in particular quadratically, - increases monotonically, in particular cubically, from the second velocity threshold to the first velocity threshold.

12. Method according to any one of claims 1 to 10, wherein When determining the incremental value as a continuous current value, a predetermined value is used which describes a square of a predetermined permanently permissible current strength of the electric current flowing at the connection.

13. Method according to any one of the preceding claims, wherein The weighting function assigns the weighting value depending on a flow rate information, which describes a flow rate of a coolant, and / or a temperature information, which describes a coolant temperature.

14. Method according to any one of the preceding claims, wherein In the initialization step, an overload value dependent on a rest time of the converter (2) is initialized, wherein, for a rest time above a rest time threshold, a predetermined start value of the overload value is initialized, and for rest times below the rest time threshold, an overload value, in particular dependent on the rest time, which is greater than the start value, is determined and initialized.

15. Method according to any one of the preceding claims, wherein the power converter (2) comprises semiconductor switching elements (7) for converting the input voltage into the output voltage, the method further comprising the following steps (S60, S70): - Determining a throttling value from the overload value; Control of the semiconductor switching elements (7) depending on the throttling value; wherein when controlling the semiconductor switching elements (7) the current at the output (5) or at the input (4) is limited if the updated overload value exceeds a predetermined overload threshold.

16. Computer program product comprising instructions which, when the program is executed by a computer, cause it to perform the steps of the method (100) according to any of the preceding claims.

17. Control device (9, 9') for an electrical power converter (2), which has two terminals, namely an input (4) for an input voltage and an output (5) for an output voltage, and is configured to convert the input voltage into the output voltage, wherein the control device (9, 9') has an initialization section (11) configured to initialize an overload value and a calculation section (12); wherein the calculation section (12) is configured to repeatedly - to obtain current information that describes the instantaneous current value of an electric current flowing at one of the terminals, - to determine a weighting value by evaluating a weighting function that assigns a weighting value to at least one current variable, using the current value as the current variable, wherein the weighting function assigns a first weighting value to values ​​of the current variable at a given current threshold and assigns a higher weighting value than the first weighting value to values ​​of the current variable above the given current threshold; - to determine an incremental value as a function of the instantaneous current value, the weighting value, and a continuous current value, such that the current has a positive influence on the magnitude of the incremental value and the continuous current value has a negative influence on the magnitude of the incremental value; and - to determine an updated overload value by cumulatively combining the previous overload value and the incremental value.

18. Power converter (2), comprising a control device (9, 9') according to claim 17 and semiconductor switching elements (7) for converting the input voltage into the output voltage.

19. Electric drive (1) for a vehicle (200), comprising an electric machine (3) and - a power converter (2) according to claim 18, which is designed as an inverter and configured to provide a multiphase alternating voltage as an output voltage to the electrical machine (3), and / or - a power converter according to claim 18, which is designed as a DC-DC converter and is configured to provide a DC voltage as an output voltage to the excitation windings of a rotor of the electric machine (3), and / or - a power converter according to claim 18, which is designed as an inverter and is configured to provide an alternating voltage as an output voltage to a primary side of an inductive high-frequency transformer for excitation windings of a rotor of the electric machine (3).

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