Method and device for operating power electronics, power electronics

Abstract

The invention relates to a method for operating power electronics (1), in particular an inverter or rectifier, which have at least one half-bridge (2) with two series-connected semiconductor switches (3, 4) and at least one intermediate circuit capacitor (6) connected in parallel with the series connection of the semiconductor switches (3, 4), wherein, in order to carry out a discharge process for electrically discharging the at least one intermediate circuit capacitor (6), the two semiconductor switches (3, 4) for generating a plurality of discharge pulses are controlled in such a way that they are simultaneously switched on for a predetermined period of time (ton) for each discharge pulse, characterised in that the semiconductor switches (3, 4) are controlled as a function of an electrical intermediate circuit voltage of the power electronics (1) applied to the intermediate circuit capacitor (6) in such a way that the pulse energy (E) of the discharge pulses of the discharge process is equal or almost equal.

Description

[0001] Description

[0002] title

[0003] Method and device for operating a power electronics system, power electronics

[0004] The invention relates to a method for operating a power electronics system, in particular an inverter or rectifier, which has at least one half-bridge with two semiconductor switches connected in series and at least one intermediate circuit capacitor connected in parallel to the series connection of the semiconductor switches, wherein in order to carry out a discharge process for electrically discharging the at least one intermediate circuit capacitor, the two semiconductor switches are controlled to generate a plurality of discharge pulses in such a way that they are simultaneously conductive for a predetermined period of time for each discharge pulse.

[0005] Furthermore, the invention relates to a device for operating such a power electronics system, which is characterized by a control unit that is specifically designed to carry out the above-mentioned method.

[0006] Furthermore, the invention relates to a power electronics system, in particular as described above, which comprises the above-mentioned device.

[0007] Furthermore, the invention relates to a computer program, a machine-readable storage medium, a drive train and a vehicle.

[0008] State of the art

[0009] Methods and devices of the type mentioned above are already known from the prior art. To discharge the intermediate circuit capacitor or the intermediate circuit, it is known to switch a half-bridge into a short circuit, in which both semiconductor switches, in particular the semiconductor switch to the positive high-voltage potential and the semiconductor switch to the negative high-voltage potential, are simultaneously switched on. In particular, it is known to switch on a so-called soft short circuit, in which one of the semiconductor switches is fully switched on and the other of the semiconductor switches is slowly switched on with the aid of a raised gate series resistor. Depending on the gate voltage of the other semiconductor switch, a half-bridge cross-current is established, which discharges the capacitance of the intermediate circuit, in particular the intermediate circuit capacitor.This cross-current is converted into short pulses, so-called discharge pulses, which are currently implemented repetitively at a fixed clock frequency. The resulting power loss is dissipated via the semiconductor switch, which slowly adjusts to the current and thus carries the full intermediate circuit voltage at the time of the discharge pulse.

[0010] Disclosure of the invention

[0011] The inventive method with the features of claim 1 has the advantage that the intermediate circuit or intermediate circuit capacitor is discharged more quickly than before. For this purpose, the invention provides that the semiconductor switches are controlled as a function of an electrical intermediate circuit voltage of the power electronics applied to the intermediate circuit capacitor in such a way that the respective pulse energy of the discharge pulses of the discharge process is the same or almost the same. It is therefore provided that within a discharge process, the discharge pulses each have the same or almost the same pulse energy, at least within this discharge process. Each discharge pulse within the discharge process thus results in the same or almost the same pulse energy.This has the advantage that even at low intermediate circuit voltages the pulse energies utilize the full potential of the power electronics and thus accelerate the discharge, and at high voltages prevent overloading of the power electronics.

[0012] According to a preferred embodiment of the invention, the duration of each discharge pulse is predetermined depending on the current intermediate circuit voltage. The pulse energy of each discharge pulse is thus adjusted depending on the current intermediate circuit voltage. As a result, each discharge pulse receives the same discharge energy as the preceding or subsequent discharge pulse, or almost the same energy.

[0013] Furthermore, it is preferably provided that the duration is specified by a pre-stored characteristic curve depending on the intermediate circuit voltage. The characteristic curve is stored, in particular, in a non-volatile memory of a control unit or control device, for example, the power electronics. The characteristic curve specifies the duration for the respective discharge pulse depending on the currently applied intermediate circuit voltage. This ensures reliable adjustment of the discharge pulses with optimized discharge energy until the intermediate circuit voltage is drained.

[0014] According to a preferred embodiment of the invention, the duration of each discharge pulse is specified as a function of a target current flowing through the half-bridge during each discharge pulse. The pulse energy of each discharge pulse is thus adjusted as a function of the target current and the current intermediate circuit voltage. As a result, each discharge pulse receives the same discharge energy as the preceding or subsequent discharge pulse, or almost the same energy.

[0015] Furthermore, it is preferably provided that the target current is specified by a pre-stored characteristic curve depending on the intermediate circuit voltage. The characteristic curve is stored, in particular, in a non-volatile memory of a control unit or control device, for example, the power electronics. The characteristic curve specifies the target current for the respective discharge pulse depending on the currently applied intermediate circuit voltage. This ensures reliable adjustment of the discharge pulses with optimal discharge energy until the intermediate circuit voltage is drained.

[0016] Particularly preferably, the characteristic curve is determined through prior testing and / or calculations and then stored as described above. The characteristic curve can also be implemented in the form of a look-up table. According to a further embodiment of the invention, it is preferably provided that the actual current is detected by feedback. This makes it possible to compare the set current with the target current and adjust it. The duration of the discharge pulse is again used as the manipulated variable for this purpose. If the target current was programmed via a characteristic curve according to the previous advantageous embodiment, it is possible to adjust the pulse energy significantly more precisely.

[0017] Furthermore, it is preferably provided that the respective pulse width or time duration is determined as a function of a pre-charging duration of a gate driver of the respective semiconductor switch. Each semiconductor switch is generally assigned a device driver, by which the respective semiconductor switch is switched conductive or non-conductive. Because the switching into conduction itself requires a certain amount of time until the threshold voltage of the semiconductor switch is exceeded and the semiconductor switch begins to consume current (here referred to as the pre-charging duration), this pre-charging duration is taken into account when determining the pulse width in order to approximately determine the actually set pulse width or current pulse width. In particular, a particularly specified or fixed amount of time corresponding to the pre-charging duration is added to the theoretical pulse width required to achieve the discharge energy.This ensures that the total pulse width includes both the desired pulse width and the pre-charge duration, ensuring the desired discharge energy is reliably achieved. The pulse width then corresponds to the total pulse width minus the pre-charge duration.

[0018] Furthermore, it is preferably provided that the respectively converted pulse energy of a discharge pulse is approximated, in particular assuming a triangular current signal, and that the set pulse width of a charging pulse following this discharge pulse is specified as a function of the converted pulse energy. The duration or pulse width of a discharge pulse is thus set or specified as a function of the pulse energy converted by a previous discharge pulse, in particular by the discharge pulse immediately preceding it, in order to achieve an optimal result with regard to the accuracy of the pulse energy by varying the semiconductor parameters. For the preferred approximation using the triangular signal, the following formula is used in particular:

[0019] E corresponds to p the pulse energy of a discharge pulse, r the measured or approximated current peak value, VDC the current intermediate circuit voltage and t the pulse width.

[0020] Preferably, an actually achieved charging pulse width or an actual duration is detected, in particular by means of a suitable sensor system, particularly preferably measured, and taken into account to specify the duration for the or a subsequent discharge pulse. Thus, depending on the actual pulse width of a discharge pulse, the duration for the or a subsequent discharge pulse is set in order to ensure the same or almost the same pulse energy.

[0021] To generate a discharge process, one of the semiconductor switches is preferably permanently conductive, while the other semiconductor switch is controlled repetitively or in a pulsed manner. In particular, the semiconductor switch is controlled continuously to the positive high-voltage potential, and the semiconductor switch is controlled in a pulsed manner to the negative high-voltage potential, or vice versa.

[0022] The device according to the invention with the features of claim 9 is characterized in that the control unit is specifically designed to carry out the method according to the invention. This results in the advantages already mentioned.

[0023] The power electronics according to the invention with the features of claim 10 is characterized in that the device is designed according to the invention. This results in the advantages already mentioned.

[0024] The computer program according to the invention with the features of claim 11 is characterized in that, when executed, it carries out the method according to the invention. This results in the advantages already mentioned.

[0025] The storage medium according to the invention with the features of claim 12 is characterized by the computer program according to the invention, which can be executed on a computer, for example on a computing unit of a control device.

[0026] The drive train according to the invention with the features of claim 13 comprises power electronics as described above, and in particular an electric motor and / or an electrical energy storage device for supplying the electric motor with electrical energy. The power electronics operate the drive train according to the method according to the invention. This results in the aforementioned advantages.

[0027] The vehicle according to the invention, in particular a motor vehicle, with the features of claim 14 is characterized by the drive train according to the invention.

[0028] Further advantages and preferred features and combinations of features emerge in particular from the above description and from the claims. The invention will be explained in more detail below with reference to the drawings.

[0029] Figure 1 shows a half-bridge of a power electronics in a simplified representation,

[0030] Figure 2A is a diagram explaining an advantageous method for operating the power electronics and

[0031] Figure 2B is a diagram explaining the timing of a discharge pulse, Figure 3A is a method in which energy pre-control is carried out as a function of the electrical current,

[0032] Figure 3B shows an embodiment of an energy control system for which a converted pulse energy is calculated and

[0033] Figure 3C shows an energy control in which a discharge pulse width is measured.

[0034] Figure 1 shows a simplified representation of power electronics 1, which is designed, for example, as an inverter for an electric machine of an electric vehicle. The power electronics 1 has a half-bridge 2, which has a first semiconductor switch 3 and a second semiconductor switch 4, which are connected in series with one another. The first semiconductor switch 3 is electrically connected, for example, to a positive potential of the supply voltage (+), in particular high voltage, and the second semiconductor switch 4 is connected to a ground connection or to a negative potential of the supply voltage (-), in particular high voltage. Phase 5 of the electric machine, for example U, V or W, is connected between the two semiconductor switches 3, 4. By controlling the semiconductor switches 3, 4, phase 5 of the electric machine can be specifically supplied with an operating current.In parallel to the series connection of the semiconductor switches 3, 4 there is also an intermediate circuit capacitor 6, across which the supply voltage VDC drops.

[0035] Each semiconductor switch 3, 4 is preceded by a so-called gate driver 7, which switches the respective semiconductor switch 3, 4 to conducting or non-conducting. In this example, the gate driver 7 is shown only for semiconductor switch 3.

[0036] To discharge the intermediate circuit capacitor 6, one of the semiconductor switches, previously semiconductor switch 4, i.e. the low-side semiconductor switch, is fully switched on and another of the semiconductor switches, i.e. semiconductor switch 3 or the high-side semiconductor switch, is operated by the gate driver 7 in a pulsed or repetitive manner for a predetermined period of time in order to create a soft short circuit. According to a further embodiment, the low-side semiconductor switch is pulsed and the high-side semiconductor switch is switched on continuously in order to carry out a discharge process. An increased gate series resistor 8 ensures that the semiconductor switch 3 is only switched on slowly. Depending on the gate voltage, a half-bridge cross-current is generated, which discharges the capacitance of the intermediate circuit capacitor 6 or the entire intermediate circuit.This cross-current is converted into short pulses by controlling the semiconductor switch 3, as indicated by a corresponding symbol in Figure 1. The pulses occur at a fixed clock frequency. The resulting power loss is dissipated via the first semiconductor switch 3, which carries the full intermediate circuit voltage at the time of the pulse and is operated in linear mode. The energy drawn from the intermediate circuit capacitor 6 is converted into heat in the semiconductor switch 3 and preferably dissipated by a cooling system of the power electronics 1. This gives rise to the problem that with constant current control, when lower intermediate circuit voltages are reached, the pulse energy no longer utilizes the full potential of the power electronics 1 and, at high voltages, tends to overload the power module 1.

[0037] Figure 2B shows the time course of the gate voltage signal and the current I of a discharge pulse.

[0038] It is proposed to approximate the current I of a discharge pulse using a triangular signal according to the following equation:

[0039] Where E_p represents the pulse energy, V_DC represents the current peak value, and t represents the duration of the discharge pulse. It can be seen that with constant peak current and pulse width, the pulse energy E decreases with decreasing intermediate circuit voltage V_DC. p decreases linearly. A slightly wider charge pulse must be applied to achieve the same current via the DIBL effect, but this does not have a significant impact on the process.

[0040] With a voltage-dependent adjustment of the current, and thus also of the pulse width, a constant pulse energy can be advantageously set for the discharge pulses of a discharge process, whereby the discharge rate of the intermediate circuit increases significantly even in the range of lower electrical voltages of the intermediate circuit, as shown by way of example in Figure 2A. The voltage curve decreases exponentially faster due to this advantageous method.

[0041] To illustrate an advantageous method for discharging the intermediate circuit, Figure 2A shows a diagram showing current I and voltage U over time t. The diagram shows the previous voltage curve VDo as well as the advantageous voltage curve with exponential decay with VDi generated by the method described below. The diagram also shows a constant discharge current Io and a charging current ii adjusted by the advantageous method, which varies between a maximum charging current i ma x and a minimum charging current i m in steps.

[0042] According to a first embodiment of the advantageous method, pre-control of the pulse energy is carried out by adjusting the charging current ii as a function of the currently applied intermediate circuit voltage VDi. For this purpose, in particular, a characteristic curve is stored in a non-volatile memory of a control unit 9, which controls the power electronics 1 and is in particular part of the power electronics 1. The characteristic curve is selected such that it determines the target current or target current range (i min - imax) and thus, with higher peak current and lower intermediate circuit voltage VDC, the pulse energy E of the discharge pulses is kept the same or approximately the same. The current is thus adjusted in such a way that the same pulse energy is always drawn from the intermediate circuit with each discharge pulse. Because the energy in the intermediate circuit capacitor 6 decreases quadratically with decreasing voltage VDC, an exponential discharge characteristic of the half-bridge 2 arises, as shown by curve VDi. According to a second embodiment, the converted pulse energy E is regulated to a setpoint according to the approximation formula mentioned above. For this purpose, the pulse width of the respective discharge pulse, i.e. the specified time duration, is used as the manipulated variable and the current level of the respective discharge pulse is varied accordingly.In particular in the control unit 9, in particular in a computing unit of the control unit 9, a current voltage value of the intermediate circuit voltage VDC, the current current peak l. pea k and the current pulse width t are determined. For the pulse width t, the control time of the output discharge pulse is subtracted from a fixed time amount tfj X , which corresponds to the elapsed time for precharging the gate of the controlled semiconductor switch 3 without current flow through the semiconductor switch 3. Thus, the precharging time tfj X taken into account to determine the actual pulse width: t = t on - tfj X

[0043] Because different batches of semiconductors 3, 4 can exhibit differing transfer characteristics, these deviations are compensated for by advantageously considering the pulse width by controlling to a constant or equal pulse energy E. This ensures that all devices receive approximately the same discharge time despite differing transfer characteristics of individual semiconductor switches.

[0044] Figures 3A to 3C show control loops to explain and summarize the methods described above.

[0045] According to the embodiment of Figure 3A, the actual current st is set as a function of the set current l S0 n is adjusted. First, the current intermediate circuit voltage VDC is measured and the corresponding target current Isoii = f (VDC) in the form of a control window of l m in and l m ax, as described above. Depending on the control difference st - Isoii is the new target pulse width or the time duration t on adjusted, at least if the actual current exceeds the control window between the minimum current l m in and the maximum current l ma x leaves. Then the time period t on preferably decremented or incremented. The discharge pulse is then set by the control unit by controlling, in particular, the semiconductor switch 3. The flowing discharge current st is measured (l me ss) and the control circuit for the subsequent pulse or the following discharge pulse. In particular, a comparator 10 of the control unit 9 compares the target current with the actual current and the pulse duration t on for the following discharge pulse.

[0046] According to the embodiment of Figure 3B, the target pulse energy Esoii is used as the basis for energy control, taking into account the actual duration or the actual pulse width tactual. In this case, the duration t is determined depending on the pulse energy for the subsequent pulse. on determined or predetermined and set by the controller or control unit 9 and in particular the semiconductor switch 3. The actual current flowing through the semiconductor bridge 2 st is measured as in the previous embodiment. In addition, the actual pulse width or the actual duration of the discharge pulse tactual is calculated. In particular, the actually set pulse width is calculated using the equation described above from the actually total set pulse width t on and the pre-charge time tfj Xcalculated. Depending on the actual current and the actual time duration tist, the last set pulse energy Eist is calculated by the control unit 9, particularly depending on the intermediate circuit voltage VDC, and fed back to the control system. Depending on the measured or calculated pulse energy Eist, the time duration for the next discharge pulse t on taking into account the minimum energy E m in and the maximum energy E ma x. Here, the pulse width is preferably set to an energy control window. If the calculated energy value is not between the minimum energy E m in and the maximum energy E ma x, the pulse duration t is preferred on incremented or decremented.

[0047] Figure 3C shows a further embodiment which differs from the previous embodiment in that the actual pulse duration tist is not calculated but measured tme ss. For this purpose, for example, a sensor device 11 is used, which monitors or measures the pulse duration tist_mess of the set discharge pulse and forms the basis for calculating the converted pulse energy Eist. This enables even more precise adjustment of the pulse energy, and any unknown influences caused by semiconductor properties or unknown semiconductor parameters can be compensated for.

Claims

Claims 1. Method for operating power electronics (1), in particular an inverter or rectifier, which has at least one half-bridge (2) with two series-connected semiconductor switches (3, 4) and at least one intermediate circuit capacitor (6) connected in parallel to the series connection of the semiconductor switches (3, 4), wherein, in order to carry out a discharge process for electrically discharging the at least one intermediate circuit capacitor (6), the two semiconductor switches (3, 4) are controlled to generate several discharge pulses such that they are open for a predetermined time period (t) for each discharge pulse. on) are simultaneously switched to conduction, characterized in that the semiconductor switches (3,4) are controlled depending on an electrical intermediate circuit voltage of the power electronics (1) applied to the intermediate circuit capacitor (6) such that the pulse energy (E) of the discharge pulses of the discharge process is equal or nearly equal.

2. Method according to claim 1, characterized in that the duration (ton) of the respective discharge pulse of the discharge process depends on the intermediate circuit voltage or a target current (l) flowing through the half-bridge (2) at each discharge pulse. S0 n) is specified.

3. Method according to claim 2, characterized in that the duration or the target current (l S0 n) is specified by a predefined characteristic curve depending on the DC link voltage (VDC).

4. Method according to claim 3, characterized in that the characteristic curve is determined in advance by tests and / or calculations and in particular is stored in a non-volatile memory of the power electronics (1).

5. Method according to one of the preceding claims, characterized in that the target current (l S0 n) depending on a The actual current (list) flowing through the half-bridge (2) is specified. Method according to claim 5, characterized in that the respective time duration (t) on ) depending on a pre-charging time (tfj X ) of a gate driver (7) of the respective semiconductor switch (3). Method according to one of the preceding claims, characterized in that the respective converted pulse energy (Eist) of a discharge pulse is approximated, in particular by means of a triangular signal, and that the predetermined time duration (t) on) of a subsequent discharge pulse depending on the converted pulse energy (Eist). Method according to one of the preceding claims, characterized in that an actually achieved discharge pulse width (fet) is detected, in particular measured, and used to specify the time duration (t). on) is taken into account. Device for operating power electronics (1), in particular an inverter or rectifier, wherein the power electronics (1) comprises at least one half-bridge (2) with two series-connected semiconductor switches (3, 4) and at least one intermediate circuit capacitor (6) connected in parallel to the series connection of the semiconductor switches (3, 4), characterized by a control unit (9) specifically configured to execute the method according to any one of claims 1 to 8. Power electronics (1), in particular an inverter or rectifier, comprising at least one half-bridge (2) with two series-connected semiconductor switches (3, 4) and at least one intermediate circuit capacitor (6), characterized by a device according to claim 9. Computer program comprising instructions which, when the computer program is executed, in particular by a device according to claim 9, executes a method according to any one of claims 1 to 8.

12. Machine-readable storage medium on which a computer program according to claim 11 is stored.

13. Powertrain comprising power electronics according to claim 10 and, in particular, an electric machine and / or an electrical energy storage device for supplying the electric machine with electrical energy.

14. Vehicle, in particular a motor vehicle, with a powertrain according to Claim 13.

Images